First of all, congratulations! While 0 A.D. is designed to be easily modifiable in principle, doing something the first time can be challenging. If you continue and become more experienced, you'll see many things turn out to be much easier than they might seem right now.
Then some minor nitpicking: 0 A.D. is free and open-source software. You can do whatever you want with it, provided you comply with the relevant licences. Most assets (e.g. art) are released under CC-BY-SA-3.0, while most code is released under GPLv2. Your mod contains both art and code, however, you only mention the former. You can release code under CC or any licence you like, if you've written it yourself. However, if you've copied it from 0 A.D. (and I believe you did), then you have to release it under GPLv2 (or v3), therefore you should make that explicit in your mod.
Furthermore, include the relevant licence files (you can just copy them from elsewhere). Although this is not really necessary, it is good practice (people can be lazy). See how it's done in https://trac.wildfiregames.com/browser/ps/trunk
Also, when using dates (e.g. in your diary.md), keep in mind some Americans might interpret 10/03/21 as October the 3rd, therefore it's advisable to either use the ISO format (2021-03-10) or to write out the month (10 March 2021) or abbreviate it (10/Mar/21).
And another suggestion: include https://code.wildfiregames.com/D3037 Many players are asking for this, unaware how to do it via the local user.cfg configuration file.
You might want to partially revert D2875, if you've not done so already.