The valve cover bolt torque is 8.5 Nm, or 6.2 lb/ft. Not very much.
Use a basic criss-cross pattern and bring them down a bit at a time.
I use a 1/4 ratchet, and just snug them down with a small bit of force. They should snug down and give a bottoming-out firm feel. Might check the threads and clean out the holes also.
The valve cover gasket will harden over time, the aftermarket ones seem to last about 2 years. So, go ahead and get a new one.
Very easy job, just snap off the plug wire covers and lay the wires out of the way; then watch for the electrical connectors along the intake side when you lay the valve cover on.

DG