1) You generally don't need sealer on the valve cover gaskets. What does happen a lot, however, is that the OEM style cork gaskets get crushed and hardened when old, and they start to leak a little, and people try to stop it by cranking down on the bolts holding the cover on some more. Which can bend the cover down where the bolts are, leading to worse leaking.

I'd suggest a new seal, installed dry, and look at the cover and gently tap it flat again if need be.

2) Not sure what sort of adjusters the rear brakes have on a '65, the brakes on my '63 PV are the manual star adjusters, hiding inside a little hole on the backing plates. I honestly forget which way they go every time I mess with them, but one way the get looser, the other tighter. 50/50, just go the other way if you get it wrong. But your description of the way the brakes are working leads me to think the drums are adjusted well enough, but perhaps something is off on the parking brake cables. Loosely adjusted rums make the pedal travel much farther than normal (and on the rear, the pedal will travel less when the hand brake is pulled).

Pulls under braking are probably more likely caused by things going on with the front brakes? Possibly some swollen flex lines (seems to happen a lot on old, OLD Volvos), possibly some slightly sticky calipers? Although those will more likely tend to drag lightly upon release, then get hot and wear the pads out quickly. Might be mismatched pads. Might just be something looser or poorly aligned on the front suspension.

3) Sounds like alignment issues. Or lousy tires. Or both. maybe it secretly wants to become a 'drift' car, and spend it's time sliding sideways turning tires into smoke.
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'63 PV544 rat rod, '93 Classic #1141 245 (now w/16V turbo)