IPS patches

Just a simple question, with conflicts in mind, how many IPS patches can you apply on a single rom without expanding it? I mean there are patches for "Flawless Victory", equipable crossbows etc so how many of these can I apply without messing my rom up?

You can apply as many patches as you want to a ROM without expanding it. The problem will be patches conflicting with each other. And as you know, it will corrupt your ROM. The "Flawless Victory" patch conflicts with pretty much every patch known to man, as do many others. My advice to you, would be to get a group of patches together that you want to use, and download this awesome new tool by mblock129 that will tell you if any of them are conflicting with each other. I have not used the tool yet, but I'm sure it's easy enough.
http://zephyr129.brinkster.net/patchconflict.html

That pretty much depends on the patch. Most patches rewrite some code in the game, or simply use free space from specific parts of the ROM to implement changes.

ROM Hacks will surely expand the ROM in order to make space for all the custom changes to it.

Just something to do as a precautionary:
Apply the patches when your game is complete. Make Backups of each patch so that way you can which conflict and which don't.
NOTHING is worse than making a huge game, and having applied a patch to it in the beginning just to find out that that patch corrupts something a million years later into the game.
Trust me, not only is it awesome watching your completed work shine with each and every patch, but hey it's safe.

But OK that's not really pertaining to the thread, nevertheless, that tool by MBlock is very nifty! Definitely use it