So, I've been away from Pokemon since X/Y and now I want to go back.

But all my good Pokemons are on HeartGold. How can I transfer them to Ultra Sun? I know about Pokemon Bank an all, but it just works with Black/White apparently.

So, I'll probably have to transfer them to Black/White first, right? How can I do it?

Most importantly, will it be too time consuming? It's more than 100 pokes. If it's too time consuming then I won't even bother.

Thanks lads.