On this page I'll show some really good resources and communities an aspiring conlanger might find useful or interesting.
books and stuff
So if you just started conlanging, the Language Construction Kit (LCK) is what most people will tell you to get. It is available on amazon for a small price, but there is an online version here: http://zompist.com/kit.html
Also on his website, there is a tool some more intermediate conlangers might want to use: the sound change applier. It's a really cool small javascript program and once you get used to the notation, it can be quite powerful. You can find the SCA² here.
To be taken more seriously by conlangers (and real linguists) you definitely should learn the IPA (not the beer, the alphabet) and interlinear gloss. Learning them might be really boring and repetitive, but afterwards you can proudly tell your mates that you're now able to perform a prenasalized glottalized lateral click. So to learn the IPA, there are several resources, but I found the most helpful to be the wikipedia page and the Interactive IPA Chart. To learn glossing, the go-to method is the Leipzig Glossing Rules, they will tell you exactly how to gloss what under which circumstances.
Now if you want to know if the features in your conlang are too wack or are perfectly naturalistic, the World Atlas of Language Structure (WALS) is your best friend. It lists several features, e.g. 'Consonant inventories', and then shows you statistics concerning that feature (in this case the size of the consonant inventory). Still, if your conlang has a feature that is very rare, consider the rule of ANADEW - A Natlang (short for natural language) Already Did It Even Worse – so you're probably fine. Another great resource is CLICS, a cross-linguistic database of colexifications around the world. Colexifications essentially refer to the case when in a language, several meanings are described with the same word; think English 'draw', which means both 'pull, drag' and 'depict with lines'. A similar yet distinct website is PHOIBLE, another cross-linguistic database which is concerned with phonological inventories around the world. Don't know whether the combinations of phonemes in your language is naturalistic? PHOIBLE can tell you whether it appears in a natlang!
When you come to the part where you want to evolve your language in several daughter languages, the Index Diachronica is what you want. A comprehensive encyclopedia of hundreds of sound changes that have happened in at least language in the world. You can even search by original sound and target sound! Still, all the information is to be taken carefully, as some changes don't have any sources. And as always with conlanging, don't take anything that sounds cool in your 'repository of sound changes that will happen from Classical Akshbtr to Early Modern Middle Akshbtr', think bigger, in categories. Nevertheless the Index Diachronica is a great source if you want to know if your sound change is original - or not. But when language changes, not only the phonology, but also the grammar changes. Therefore the World Lexicon of Grammaticalization was created, listing many different grammaticalizations, for example how you can derive a comparative from an ablative. The PDF is available here. Now there are many more great resources, but the ones listed above are a good start. One way or the other, if you have a specific question, you're better off asking in one of those lovely communities:
communities
There are some great communities out there dedicated to conlanging albeit it being a quite niche hobby. First of all I'll list the communities of which I'm part and of which I can definitely say that they're very nice and welcoming.
First of all the r/conlangs reddit community. With over 60k members it's pretty large, and thus you'll always find someone who either can help you or whom you can help. Associated with the subreddit, the CDN (Conlanging Discord Network) is one of the best discord servers for conlangers - and I speak from experience. With many specialized people and extra channels for neography and worldbuilding, you'll certainly find somebody to answer your questions. Another server - whose activity has sadly declined in recent months - is the Conlangs discord server, which is not affiliated with the subreddit albeit the similar name. It's a bit smaller but that tightens the relation and trust between community members, which is undoubtedly pretty cool. Also I absolutely have to mention the LCS - the Language Creation Society - who made it possible that this whole webpage even exists (thanks again!). With 145 members in 22 countries and a bi-annual conference and many benefits for its members (you can even get a flag, how cool is that!), it's another great community for (would-be) conlangers.
Other communities I'm not actively part of are the CBB - an internet forum dedicated to all sorts of worldbuilding, including conlanging, the ZBB - another bulletin board lead by Mark Rosenfelder, who wrote the LCK, the CONLANG-L mailing list - founded in 1991, making it the oldest conlanging community and finally the CWS - a website where you can create and store your conlangs.
So that's about it, all the resources and communities I can think of. If you don't know which one to choose, just check them out - I swear they're nice!