Just use a jigsaw and keep to the line. If you take it slowly you will get a nice clean line. Far cheaper option than buying a table or band saw.

would i be able to fit a 4 bar lifter in with 75mm wheels?

I dont know, design one to fit in the space. That is half the fun of building robots!

if i decide to go for a spinner whats the smallest size spinning disk you would recommend

How long is a piece of string?

I would recommend for your first spinner, 25cm diameter and 1000rpm. It wont be spectacular but it will allow you to understand all the problems that crop up with a spinning disc.