My best crappie fishing was in a 17' aluminum tiller steer boat. Small enough to put it where you want it, heavy enough to be stable.
I wouldn't buy a new boat, lots of good, lightly used models out there. Some decent rods and reels (which can be relatively inexpensive for Crappie)
I bought a bigger boat and miss my first one. The best size and type boat depends on your preferred style of fishing. I'm a single pole jigger for the most part.

The folks I talk to say Livescope is a game changer. Get it if you can spend the $$ on it. I'm strongly considering it.