Don't be afraid to use a [rubber] mallet with the Lee Loader to help resize the hulls and get them into the sizing body without too much exertion. Just go slow and don't get carried away. (using modest taps and not heavy blows!).
As for the load chart, that will "complete" a lee Loader, but is perfectly safe to also get load recipes from a shotshell reloading manual too. In the 20ga use 7/8oz or 1oz data. As for "pressure" when charging and seating over-powder wads, firm compression usually suffices. Just don't exceed recommended amount of powder!