You should not use any sealant for the sump gasket or the jugs gasket. Surface prep is very important............must be completely clean.
Use caution with the sump gasket bolts..............7 ft-lbs maximum.
Yes, you could check the torque on the head studs. Actually as part of a re-build, you should be re-checking the torques. Re-check at first day after running...............re-check at about 170 kms................re-check again after another 170 kms.............lastly check again after another 170 kms. 30 ft-lbs should be used for the 8 large acorn nuts, and 14 ft-lbs for the 4 smaller on the head a well as the 2 under the spark plugs .