A friend gave me an old Polynesian three person spa. He was having trouble with the temperature and was quoted $600 to fix the problem. I found a new thermostat and have it on order. The motor is working fine and everything else seems in working order although the wood looks horrible. I have a few questions?

Can I put in a new more powerful motor to increase the water flow?

How hard is it to add new jets?

What can I do to make the wood look better? Paint? Refinish? Linseed oil?