i am in the process of doing the same conversion... i suggest doing the heater hoses... because in the s13 chassis they are a bitch to get too... do it while the motor is out of the car...
but same as above... change all the servicable items new fuel filter, change the transmission oil, diff oil, spark plugs, air filter etc
you will need to mod your power steer lines and pump (unless you get a non hicas p/s pump)...
but some more info would be a good start...