I'm worried about the legal side of things regarding software licensing and stuff.
Software licensing is for the most part really easy - it's similar to how you'd go groceries shopping. As said before there are many free alternatives, but even there you need to make sure that it's allowed to use it for commercial purposes, some example of such software would be GIMP, Blender, Code::Blocks, etc. For payed software you just need to make sure what the license allows you to do. Many applications have a "per desk" policy, which means you can only install it on one computer and need another license if you want to install it somewhere else. Some come with a license for two desks, so you could install it on your notebook and desktop for example. If something is not clear about a certain software, it's usually rather easy to contact the author or the support team.
That's for software application, however for library licenses things are very similar and it's mostly easier to understand, due to the usage of standardized licenses. If you find a library you'd like to use, you'll simply have to look up the license and there are many sites that break the legal gibberish into something understandable (e.g.
TLDRLegal). Be aware that "Commercial Use" does not automatically mean, you can use it however you want, instead you need to see under which conditions you can use it commercially. For instance GPL allows for commercial usage, if you put your own software under GPL and make your source code available to the public, whereas with zlib/libpng (which SFML uses), you can do anything as long as you don't claim to be the original author.
This might now still seem rather complex and yes there are a few things you'll have to look up/learn, but overall it's not that complex.
Regarding legal I'd say things like registering your indie company, paying business taxes and other fees (depending on country - healt care, pension fund, insurances, etc) correctly, is quite a bit more complicated and I wouldn't be sure, if I could figure all that out on my own, or if I'd hire someone to go over it.
