Mike... , naturally when the pistol shot distances increase, the added sight radius of the full size pistols helps, but realistically, your G19 should work fine.. make sure you get a good set of sight as the factory Glock sights are terrible... as for the shotgun, if you can find a used Rem 1100/1187 reasonable, they shoot pretty soft and there are a ton of aftermarket parts available... they do have some liabilities, typically the bolt carrier to recoil spring link (tuning fork) and the extended loading gates are sometime an iffy addition... I shot one for many years, and if you have a choice, the 1187 extractor is much thicker than the 1100....make sure your shotgun barrel has screw in chokes... I like the shorter barrels 21" or 24".. you may need to work on the gas ports to shoot lower power "cheap" shotshells...my M1S90 is about 10 years old and was in the $800 range... with the newer M2 guns on the market they may be available used.. again, make sure it has screw in chokes...most of the guys like the VersaMax, I have not had any experience with one as well as the Beretta 1301 or the Stoger
I'd look at your local match to get an idea of the shotshell holders you may need... speed is with the load2/load4 clips, but they are pricey, and if I were match director, would throw in a prone stage to see how practical they really are... most matches do not require prone positions, but angled roof tops are becoming popular... at the recent Area 6 multigun match, there was not a tremendous advantage to the load2 system over the trays
down the line, look for a jogging stroller, or some way to transport your stuff...two long guns, 100 rounds of 12ga, 200 rounds of pistol ammo, 200 rounds of rifle ammo, water, extra mags and equipment is easier to push than carry
good luck