make sure the carbs/injectors are clean..and test your overheat alarm. check all fuel lines for dry rot..and all electrical connections for loose or corrosion. also change gear case oil and check for water intrusion.
you need to give me the year and model number of the motor for more specific info. 200 johnson could be anything.
Ground the tan wire at the sensor, should pick up a good manual best money spent
near the top center of each head cover should be a sensor with a tan wire coming out of it.
just the impeller should be fine, so long as the rest of the pump housing is ok. sounds like you about got it covered.
if you want to get a DVA adapter so you can test the stator and powerpack and regulator/rectifier, coils..there are 2 links in my sig, one is for a cheap dva adapter, the other is a free test guide. this will help to find a weaking stator or coils or spot a bad regulator/rectifier before it damages the stator or leaves you stranded.
you actually need 2 one that measures foot pounds and one that measures in inch pounds, the only nut that requires 150lbs is the flywheel nut heads are generally 20 to 22 lbs
I would say without checking you would be fine with that there are 18 head bolts starting in the middle at 1 there is a circling sequence /for torquing most heads have those numbers embossed on them, Are you sure your up to these tasks? most head bolts are 7/16ths