MM* is one of those games where you end up with more money than you could possibly spend by the end - even more so with a solo run. I'd save my skill points and not bother with Merchant, unless you really want more early, but even that should move quickly in solo.
Anything that reduces your reaction time is good, especially in solo: expert Leather is definitely worth it, even if you're not a traditional armour-wearing class.
I don't think Staff is worthwhile - can't Necros use Daggers? Faster and better damage