For non-TTY head bolts and studs, after going through the entire torque sequence I'll always wait a half day or so and then go back in sequence and one at a time back them off about 1/4 turn, and then retorque to the final value (note-- go in sequence one at a time doing the loosen/tighten, don't loosen all of them at once!) The reason to slightly loosen them before retorquing them is because the breakaway torque needed to get them moving can often exceed the desired final torque spec, so if you try to simply tighten them again you'll get incorrect torque/tension. If you put paint witness marks on the cylinder head and bolt head (or nut if you used studs) before doing this you'll see they always take a little bit more on the loosening/retorquing cycle. If you're installing them into a block with a wet deck where the fasteners go into the cooling jacket you have to use a non-hardening sealer on the threads to do this, because if you use a hardening sealer you'll disturb the sealer when you loosen and retighten the head bolts and will probably have coolant leaks. No worries about this on a dry deck block where the head fasteners do not get into the cooling jackets. Also, if the fasteners are new and non-TTY it's not a bad idea to go through 3 torque/loosen/torque cycles on the first go around as it will burnish the threads, then let them sit half a day to a day, then come back and do the final loosen/retorque cycle.
Note: this used to be a lot more important with composite head gaskets, where the fasteners would always move an appreciable additional amount in the delayed loosen/retorque cycle since the composite head gaskets would compress a decent amount before taking a set. With modern MLS gaskets being far less compressible since they're spring steel, once the embossed layers are flattened they "hit a wall" and I've found things move a lot less and you can often get away with the initial 3 torque/loosen/torque cycles to burnish in the fasteners and not have to come back a half day to a day later to do one more loosen/torque cycle.
For TTY head bolts, one and done. You are stretching the bolt into the plastic deformation range on the first torque + angle cycle resulting in permanent elongation of the fastener and once you've done that any further cycling to the specified torque + angle only stretches the bolts further which reduces their cross sectional area and therefore reduces their ultimate strength which is what you do NOT want to do-- that's why TTY bolts are one time use.
As far as sealer on MLS gaskets, if the surface finish and flatness on the deck and heads is correct and the gasket is new with the proper viton sealing material applied where needed by the gasket manufacturer, I never use additional sealer (the exception being a little dab of RTV at the corners of the head gasket where the block/head/intake manifold meet at the corner of the valley on older engines.) I also try not to reuse MLS gaskets because while the steel portion of the gasket is typically OK, some of the viton sealer used around the cooling holes usually comes off the gasket when you try and reuse them. The only time I'll use copper coat or similar is when reusing an MLS gasket (or if the deck and cylinder head surface finish is marginal for an MLS gasket, but at that point it's better to resurface them to get the surface finish in spec), and reusing MLS gaskets is something usually only reserved for drag-only engines that see frequent teardowns and rebuilds. For an engine that's not going to see frequent rebuilds, just buy new gaskets... because it really sucks to try to save $100 and reuse a set of MLS gaskets only to find a coolant weep from a damaged viton sealing bead after you get it back together and running and then you have to pull the engine and tear the heads off again.
As far as aftermarket gaskets... modern OEM MLS gaskets are usually very well made and were designed with the proper amount of layers and shape to have proper clamp load to seal very sell given the deck and head configuration. Cometic makes good gaskets, but on modern stuff they typically aren't needed unless you're doing an extreme build or the OEM gasket has been shown to have problems in that application at your targeted power level. For example, when building an LS engine for boost rather than spending tons of money for specialty aftermarket head gaskets, a typical recommendation is to use the OEM LS9 head gaskets which were made for boost and are quite a bit cheaper than the aftermarket gaskets. The LS9 head gaskets were made for a boosted application and have additional steel layers compared the standard LS1/LS2/LS3 head gaskets. Use of aftermarket specialty head gaskets really depends on the application and intended power / cylinder pressure goals.
Disclaimer: I'm not a full time engine builder, but do usually spec out and assemble 1 or 2 engines a year for people, and work with a couple of machine shops and builders who have built engines for teams that have won numerous national championships in various racing divisions over the years, and have picked up lots of little tips from them along the way... There's always more to learn though.
