I'd make sure he wasn't terminated in a manner that's unlawful. very few reasons in Texas, but the federal laws can apply above 15 employees - so race, religion, ethnicity, age, gender, sex, etc. Best evidence is systemic practice looking at who else is fired, who is retained. sounds like a small company though so I'd expect squat.
I'd make sure the bonus isn't written in a handbook or policy as already having been earned and payable even though terminated.
make sure all expense reports are submitted and paid.
make sure you get COBRA or state continuation compliance if not pay.
$25,000 / 3 months isn't a lot for a non-compete, but if he's dead ass certain he won't compete that's free money. don't assume it's not enforceable. Texas courts will ABSOLUTELY enforce them, and even rewrite them to be enforceable when they go too far. devil is in the details on whether it's enforceable yes territory, time and scope are important but so is the company's need to prohibit competition and other factors. pay to sideline a guy isn't really what carries the day.
NDA - yes get industry knowledge, general know how and relationships excepted. you can't walk out of the company with a customer list but you can't be prohibited from talking to someone just because an NDA.
non-solicitation - you can be prohibited from talking to certain people - employees and customers if you sign a non-solicitation - this one can be more dicey than the non-compete in terms of impact on your friend. read carefully.
non-disparagement - fine, make it mutual.
good reference? good luck. I mean if you can get it, get it. most will simply confirm you worked there and dates. non-disparagement would prevent saying bad things. being fired makes a good reference hard to rely on, try and get it. don't expect it.
property - if the computer was purchased with his money it's his, but he has to work through getting work stuff off. if it's company purchased, he's got to delete or transfer his info and give it back no matter what. un-comingling data can be the basis of a trade secret lawsuit for larger dollar amounts in and of itself.
what else? I think that's most of it.