Definitely get the right size Cleco's and a pair of pliers. Better even, is to spring for a couple handful of the 3/32 size (uses a #40 drill bit), to use while you are laying out and roughing out your lines, as the holes will be pretty easy to freehand with a #40 drill bit. If you walk the hole a wee smidge out of line, the holes still line up great when you drill to final size.
On a long seam, Cleco every second or third hole, rivet the empty ones, and then remove the Clecos, or move them to other holes in the pattern, if you have lots of holes, and limited Clecos. Simple trick to avoid having the holes get progressively out of alignment as you go down the seam. Watched a very unhappy co-worker destroy an expensive helicopter panel over just such, trying to force the alignment back after it was way too late! Fit up your panels, drill the holes, deburr them, then get the final assemble underway.
Dig around the interwebs for a copy of the AC 43.13 Structural manual, and read the info on rivets and riveting, their is a lot of good info there, not only for Aircraft repair.
Heck, here ya go!
https://www.faa.gov/documentlibrary/media/advisory_circular/ac_43.13-1b_w-chg1.pdf
Off the top of my head, the rivet sizes are denoted by two numbers, (aka "Dash Numbers". The first is the diameter, in 1/32 increments, IIRC, the second is the usable shank length (measured from the head on countersunk rivets, and from under the head on domed ones) in 1/16ths of an inch. If you know the thickness, and the diameter you need, you can decide what size you want on hand in advance so as to get the normal 1 1/2 diameters of protrusion.
I have done, I would estimate, a bunch over my body weight in installed solid rivets, Spent the last 12 years I worked, doing aircraft structures work in the Forces. My last riveting project was grafting two sections of Land Rover hard top roofs together so a friend could get a relatively reliable fit from the windshield top seal. We cut the front off a roof that was damaged, and was the wrong length, but matched the windshield frame, and added that to the front of a used roof of the correct length, but was for a later series machine.
I'll double down on Aircraft Spruce and Specialty! Get their catalog! Anyone around here that can flip through it and not get a BUNCH of ideas start going off in their heads like fireworks, is likely to need to be watered rather than fed, if ya catch my drift.
ALL sorts of solutions to problems you probably did know you had! Lots of used tools to be found on ebay too. I paid less than $100 for a recoil damping pro grade 3X size rivet gun that the supplier said did not run (as he apparently, I figured) just hooked it to air and tried it without a tool in it... Worst case, as I saw it, if I had to have it overhauled and pay less than half the new price, it'd still have been a deal! A crappy old cheap air hammer can be worked with, though the triggers on them are a lot harder to control when you want to have things turn out 'just so'. They have some pretty flash, high priced stuff, but I found that their prices on stuff like rivets and tools was pretty decent, and, you know that the tools will fit!
It helps a bit to understand the way a rivet reacts to the force applied. If you are hand setting them esp., as, if you apply a bunch of light hammer strikes, the end you are hitting tends to peen over without expanding the rivet to grip the panel. Handy if you want to use that rivet for a hinge, but if you wan the rivet to set properly, a fairly sharp single blow, will expand the whole length of the shank of the rivet to grip the hole sides, as well as to form the head. We used to use a steel or aluminum block drilled to take a regular rivet snap from our pneumatic rivet guns, for most hand setting. With care we could use a flat nosed punch to avoid a mis-strike dinging up the work. As suggested too, , if you are not really concerned about the rivet heads meeting a particular spec or Standard, you can save on the rivet snaps, and just form a near enough depression on a block of steel to be held in the bench vise, or just sat on the work bench.