Reckon you've noticed that your question calls for a Ford versus Chevy discussion, Russ... so one thing to keep in the back of your mind is that YOUR preference is the single most important factor.
That said, think Big Hext has got ya one the right track. Gambler or upscale gunfighter would likely have a big-bore back-up like the birdshead Vaquero you've got, another belt pistol and rifle chambered for the same cartridge. You'd likely find a 4½" or a 5½" Vaquero would be a decent match.
Many prefer having the same grip on both pistols, some even the same barrel length... and there's some benefit to that. FWIW, I don't "do as I say" -- I use a 4½" standard Vaquero and a 5½" Bisley Vaquero. I suspect maybe a character like yours might have chosen the hide-out gun for ease of concealment, not necessarily to match the belt gun in speed or accuracy.
Your comment about not wanting to buy something that costs you a lot of gunsmithing fees is right on the mark. I can't speak to the Colt clones, but for the Rugers, it's pretty much a standard deal that you simply swap the hammer, trigger return, and base pin latch springs out (e.g., with a Wolff spring kit, less than $10 if I remember right), and get to shootin'. You can do it yourself, and after you've done it once it'll only take you about 15 minutes per gun from then on.
The cross-draw or shoulder holster will be an issue for you. Safety dictates you'll rotate your body while drawing, to keep from sweeping folks behind or to the side of you. Nor will you want to sweep your own arm from the shoulder holster. Not overwhelmingly difficult, but ya gotta make it second nature.
When it comes to rifles... the fastest/most popular are the Winchester 73, Marlin 1894, and maybe the Improved Henry (Winchester 66). Another decent one is the Winchester 92. Most folks find the Winchester 94 and the Henry a bit slower. The 94 Trapper I had was a darned fine gun, but the action never did get smooth enough to go fast. You could hunt deer with a 73 or an 1894 chambered for .45 Colt. No need to soup it up to exceed 73 design capabilities; the original .44 WCF was quite sufficient for deer, so the .45 should do you nicely as well. You might want to add a tang sight for that, though... Both 73 clones and Marlin 1894 models come in several variations, so you might first look at the Marlin, Cimarron, Navy Arms, etc. websites to see what's available.
Later on, when you're ready to go elk hunting, you can shop on the Winchester/Browning 86s or the Marlin 336/1895s... and that can be your "long-range rifle-caliber" gun for side matches
As to shotguns... gotta admit, I prefer a hammerless double, and I think that'd be in keeping with your character if you choose the Marlin 1894 rifle. OTOH, if you go with a 73, a hammer double would be closer in time. Nothing stopping folks from mixing and matching, of course, and it wouldn't be abnormal to see somebody using an old shotgun even if they had newer sidearms or rifles. Not sure you'd have to go with the coach gun length, though; many find the longer barrels swing more smoothly, aren't as jerky. And if you ever wanted to use the thing for casual trap/skeet/sporting clays the longer barrel would be more useful (similar to your reasoning about getting a deer rifle outa all this). If you go with longer barrels for that kind of reasoning, screw-in choke tubes would be a useful touch.
Double shotguns are easily broken down and stuffed into a short case for riverboat or stagecoach travel.
Good luck, and have fun shopping! -Chris