A/ Is a blog a good idea for this?
B/ Can I set up a blog for this purpose for free?
C/ Where is best for me to start/ which site or such should I look into?
D/ Any other advice?
You've already had other good comments, but I wanted to aim at something a little more comprehensive, with an eye to having a starting point for something to point to later. So hi, here, info!
(For background, I've had a blog or something similar on one or more platforms since something like 1999 or 2000. I use WordPress, on a self-hosted site, which runs me about $15 a month for hosting plus the yearly domain cost, which is $15-20ish, depending on some options, plus a paid Dreamwidth account. There are hosting plans that would be fine for a single blog for personal use that run $3-5 a month plus the domain.)
What do you want a blog for? By which I mean, "do you want to engage with people via the blog, with (hopefully) comments and discussion" or "are you looking for somewhere to put your thoughts, and you don't care as much about whether discussion happens there".
If you want somewhere to share thoughts, you probably have more options (in terms of platforms/technology) than if you want to actively encourage/engage in conversation. Discussion also comes with some considerations around moderation. (At a bare minimum, you will need to deal with spam comments, which will come find you long before anyone comments on your posts.)
Blogging culture is also different now than it was 5 or 10 years ago (though I've seen a number of people calling for a return to long-form posting in various ways, and I hope that takes off).
If you want conversation, you need to figure out how to get people to come to your site and comment there (rather than the social media sites they're already on). There are ways to do that, but you usually need to be offering something of interest (so 'random thoughts on topic' may not work, but 'unusual take on topic' can. As can 'detailed thoughtful analysis of topic'). For people to keep discussing, there also needs to be some kind of feedback loop - whether that's you replying to comments, or other people (and again, initially, that's going to be you.)
It's worth thinking about how people would find your blog. If it's you saying in some other space "Hey, I wrote this thing", and pointing at a post (like I do with my Seeking site, where I can answer, and then point to another article or six on the site and spare myself 1500+ words of typing), then that's one way people find it, and that's pretty straightforward. (See the "recently blogged" thread here for another option, or links people post to Twitter/Facebook/whatever.)
If you want people to find it on their own, that's a whole different set of concerns. Realistically, probably not going to happen a ton unless you're engaged with a community of people, or actively and regularly reaching out for connections, or maybe considering things like advertisements. It's a really big Internet out there, there's a lot of stuff on it, people are probably not going to randomly find yours, at least not in meaningful numbers, without some help.
Can you set up a blog for freeYes, but there are some other kinds of costs associated. Free sites will often include advertising (to readers) which can be off-putting and annoying. They also usually have limits on what you can do with the site, which usually comes out in terms of styles (you'll have some choices, but not as many as a site you pay for), tools (you may have some tools, but not as many as paid sites), or other flexibility.
When you're getting started, this isn't a big deal, and if you want something mostly for your own benefit, it's not a big deal, but if you think you might eventually like to make it into a larger project, you can make some choices now to make expanding easier later.
Most ad-supported online spaces are very very unstable in a business sense, because if there are ads on the content, you are not the end user, the people who look at the ads are. That means the site will make choices based on what gets them ad revenue, rather than what's best for the people making the content (or for that matter, reading/watching the content tht isn't ads). That can mean fairly sudden changes in policy, or (if badly managed) sites going under with little warning, or changing focus drastically.
What are the options?First, I strongly advise picking an option where you can get your content out if/when you want to. That means some sort of download/export option, ideally one you can do at regular intervals, like every 3-6 months. Part of the reason people self-host is to get this level of control.
You do not want to build an audience, and then be at the whim of a company who decides to sell, dramatically change their policies, or who simply goes out of business rapidly. (And you don't want to lose all your writing!) Tumblr made some significant changes about a year ago that have lead to a lot of contact getting flagged as inappropriate (since they're using a poorly-designed automated system, a lot of them are incorrectly flagged) leading people to leave the site.
If you'd like to connect with other people, look for a site that lets you do that. Tumblr is an option, my preference is Dreamwidth (bias note: one of the co-founders is a longtime dear friend), and there are periodic other tools that pop up and may or may not succeed. If you want this, you're looking for a site that makes it easy to find other people using the site in various ways, and to link to/connect to/comment on their stuff.
For example, on Dreamwidth, you can comment on other people's posts, there are periodic friending memes to find people of similar interests, there are communities with particular topics. On Tumblr, people reblog posts from other people, and that's a way you connect to others. Blogger, WordPress, and many other blog-focused sites (as opposed to social journalling/social media) make it harder to interconnect with other people.
What to look forIn general, I'd check out multiple sites
1) Can you expand this in the future?
2) How do you connect to other people?
3) What do their terms of service say? Do you understand them and what it means for your content?
4) Can you do all the things you want? (for example, if you want to have certain kinds of content - video, audio, etc - some sites will have more limits than others).
5) Can you set up a style/etc. that you like or at least don't hate? (since you may have a limited number of options with free tools).
6) What is the help information like? Sometimes that is the site's internal info, sometimes there are external user communities who are great. (This is a thing Reddit can actually be great for, if it's well moderated, but there are plenty of other options)
7) Do a little research about the site - are there concerns it might be sunsetted? (I'd be a little cautious about Blogger these days, for example, and Tumblr has been struggling.) You're looking for active development and support from the people who run the place.
Personal recommendationsIf you think you might want to, the
WordPress.com option (free hosting or paid for additional options) can be easily transitioned to hosting your own site in the future, and WordPress has a large and stable community of resources.
If you think you might like to build connections, I am partial to
Dreamwidth, in large part because their business model is explicitly "We want to keep being the neighborhood restaurant of your social media: stable, reliable, and not trying to take over the world". It does have a number of quirks, but it does the stuff it focuses on really well, and it's under ongoing if slow development.