I prefer having a number pad because I have shortcuts mapped to it. By silicone sleeve I assume you mean a keyboard cover that has the FCP shortcuts printed on it? I find them useless because I customize my keyboard. Even if I didn't customize my keyboard it doesn't take very long to memorize the single layer of shortcuts the covers illustrate. If you don't edit very frequently they can be useful though.
It's becoming less and less of an issue as computers get more powerful (but then, footage is getting much heavier), but wireless keyboards suck up more CPU and RAM than wired keyboards, which could affect performance.
Also, depending on how critical the timing is, wireless keyboards can have a delay between keypress and action, so if you're doing on-the-fly cuts or something along those lines, it could be a hassle.