I've never done that, bought a new gun so that I could buy all the reloading tools!
Hands down, I don't think you can find a better press for the dollar than the Lee Load-All II. I have the MEC Slugger, an excellent press for that purpose, but I cannot see replacing my LAII with a MEC for 12 gauge shotshells. The story might be different if I was a hardcore trap/sheet, but the jump would be to a progressive press for that. Lee offers a template for an LAII base that will allow the press to use their bench plate.
RB offered some great advice, especially the reference to Ballistic Products
. If you went with the LAII, their instructions cover using the press and the basics of hull reloading well. The big difference in hull vs. metallic reloading is that you don't wander from the components listed. You probably have pistol powders on hand, and as a start to minimize the cost, I would look at the manufacturer's website to see what hull data they list for those particular powders. What will need to be matched, being you already have the powder, is the hull, wad, and shot weight. There are wad substitution charts that allow a switch that won't upset the component column height. The powder company should have a list, a pdf download usually. That component column height is everything; otherwise, you won't be able to get the adequately folded star to close your hull.
If I give up on manual and manufacture data, looking through BP's Load of the Week Archived Data
has yielded results that have helped, and you go directly to the listed components and buy them.
My LAII lineup has 12G 2¾" BB loads (hogs) and continuing work with the STI slugs. I want to look at slug with the star crimp again, my records say that it has done better than the roll crimp and MEC folded crimp, I will sell the MEC Slugger.