FWIW,
I’ve been using the copper based anti seize on bolts since I was a kid, been torquing bolts with said anti seize on said bolts that either went into steel or aluminum with the same 1/2” drive Proto torque wrench my Dad gave me when I was 15 years old, that wrench has never been dropped, or left with a torque number dialed into it, and have torqued bolts with as little as 5# on up to 150# which is its rating, I use a 1/4” drive 160 INCH pound torque wrench, up to 13 fl lb when working with smaller fasteners, it is interesting that the spark plugs come tight and the torque wrench clicks right at about a 1/2 turn after the crush washer contacts the plug seat. Also as a FYI, crush washers are a single use item, or in an emergency can be used over then replaced as soon as practical.
So, if one is worried about too much tension applied with a torque wrench with anti seize on the threads of the plug then just use the 1/2 turn method like
@Ronnie mentioned once the crush washer comes into contact with the plug seat, and, you will have the spec’d torque per the manual. For use in the marine environment, I will always use either antiseize or thread sealant to make sure nothing corrodes.
And personally, I‘d pay the shop the $2200 to do the job, you will have a warranty on those repairs for a period of time, and if it gets messed up they have to fix it. Also, if you’ve not pulled your pumps it would be a great time to pull them and make sure you have adequate grease in the cones.
Either way, hope you can get it all done and get back on the water ASAP!