Finished the romhacking tutorials I could find and still got a question

Hello,

Coming from RMXP and trying to get into romhacking, I'm a complete noob.

therefore I read as many posts as I possibly could but there's something I'm not totally sure about.

So I want to try to make a game with firered as a base rom and it seems like Leon and UltimaSoul's FireRed Base is the most recent/complete. However it doesn't seem to have the fairy type or special/physical split like MrDollSteak's Decap. and Attack Rombase does, or does it?

Anyway my question is: are both roms compatible? Like can I use both at the same time or not? If yes, how?

Also if we later get patches for gen 8 mons (or if I make them), can I patch them into those baseroms or will those patches be compatible with them? Which ro is better if I'm considering adding changes like that myself?

Thanks very much in advance if there are any kind of answer to any of those questions :)

You cannot use both ROMs together. The way ROM hacking works in general is that you take a basic ROM and add additions to it. For example, extra flags to store more data/events, changes, etc. Something like an extra flag hack can be combined with a ROM base usually because it's a small piece of ASM code which you can change the offsets on. For example, instead of putting such code at a usual point like 0x800000, you can change it, because it might only be a few hundred bytes. For a ROM base however, months or years go into adding MANY new things like this, extra flag, different pokemon battle systems, etc. Because of the complexity of most ROM bases, they even increase the limit of the game from the usual 16MB to 32MB. Most of this space is never used, however, a 1 or 2MB chunk or more usually is. This is a very large amount of data, and since most of this data contains references to other data, it would be impossible for anyone not really dedicated, or not being a well-organized author, to change. Theoretically, if you knew all the work done, all the offsets and references that were changed, then you could change it.

Okay thank you very very much for the clarification! :)

What would any of you recommend me as baserom?