timing belt
tensioner
water pump
tensioner spring
stick with OEM for all of the above
If you are wanting to improve cooling then do so with a larger / thicker radiator, as far as i am aware there is no aftermarket "uprated" water pump available. you can have the fins on the oem water pump trimmed to reduce high rpm cavitation but this is only if you are running silly revs........
timing belt is fine as OEM even with aftermarket cams. an additional tensioner can be added to the exhaust side to prevent belt whip if you were being really fussy
Don't high lift cams and stronger valve springs place extra stress on an OEM Timing Belt - can you explain this more.