91 sw20, done 112,000km. To change the engine seals, water pump, timing belt, timing belt tensioner, does the engine need to be out? Is there anything else I should do at the same time? It's my first MR2 so I'm learning as I go, performance isn't a huge issue, happy to keep the car stock. Appreciate advice?

Engine out is a lot easier.
Drop the whole rear subframe, suspension and engine +gearbox as one :)

Do you intend to do it yourself?
 
Either NA or turbo, can be done in the car.
Check out:
http://www.mrtwo.net/mr2modproject/service/timingbelt/timingbelt.htm

 
Also note that Gen 2 timing belts are different to Gen 3 belts that have one extra tooth.
 
 
 
 
 
 
 

Was going to do what I could myself.

Can be done in the car as others have said.  I would personally take the engine out and would think about a clutch kit at the same time if yours is unknown simply for the peace of mind esp if keeping the car.