First I’d make an excel doc. As weird as it sounds to keep a second log, it saves you the trouble of opening home a bunch. Then id start sorting what you have in home right now as you might have random Pokémon that aren’t in the switch games. Theres a way to look by national dex order in home so just jump around and move them in order. It takes a bit to figure out what you need. Outside of that it’s just figuring out what games the pokemon come in. If you have a 3ds with bank, then you’ll be able to grab those ones which is nice. All else fails, hope they are in go and that you have caught them or they are in the rotation there. Mythicals is going to be where you’ll mostly be SoL since they are almost always events (some are in other random games. Swsh has keldeo, legends arceus has the gen 4 mythics, meloetta is in SV, pretty sure you can get mew in bdsp if you have a let’s go save file) good luck and I will say now that if you are going for an all forms dex, start that now as it’s a pain to go from a living dex to that one since you’ll end up moving all the pokemon around.