How would you insulate these exterior walls without cutting more drywall?

You aren't going to have much luck fishing batts up from the bottom. Between the friction against the studs and the wiring you just ran, those batts are going to bunch up, snag, and leave huge uninsulated gaps at the top where you need the coverage most. If you try to force them, you're likely to pull a staple loose or kink your new Romex. It's a frustrating process that rarely results in a solid thermal envelope.

Your best bet for a minimal-hole approach is **dense pack cellulose** or fiberglass. Since you have the bottoms open, you can use the tube injection method. You'll need to rent a proffesional-grade blower and get a long, flexible 2-inch hose. You snake that hose all the way to the top of the stud bay through your bottom opening. As the machine pumps, you slowly pull the hose down, "packing" the cavity from the top down. This fills in around the wires much better than batts ever coud. But there is a catch. If your house has fire blocking—those horizontal 2x4s midway up the wall—the tube is going to hit a dead end. You whould have to drill a hole above every fire block to get the rest of the cavity filled. Even without fire blocks, getting a hose around the top plates and into those narrow gaps by the windows is tricky without seeing what you're doing. You might end up needing a few 2-inch holes near the ceiling anyway to ensure the very top of the wall isn't a total heat sink. Honestly, if it's just a couple of walls, I'd reconsider just taking the drywall down. By the time you rent the blower, wrestle with a hose that's snagging on your new wires, and patch the inevitable "oops" holes, you could have hung new sheets. Plus, you can't properly **air seal** or add a vapor retarder with blown-in. If you live in a cold climate, that air sealing is just as important as the R-value of the insulation itself. If you're dead set on not cutting more, just make sure you use a high-pressure blower. The cheap units from big box stores often don't have enough power to pack cellulose tight enough to prevent settling. If it settles, you’ll have a six-inch gap of cold air at the top of every wall in a few years.

I never even thought about fire blocks. Is there a way to check if I have those without cutting a hole just to see? Maybe a stud finder woud pick up a horizontal beam if I ran it vertically? Also, that settling issue sounds like a nightmare. If I go with the dense pack stuff, how do I actually know it's packed tight enough if I can't see inside? I don't want to be doing this all over again in five years beacuse the top of the wall is empty. Does the blower machine have a gauge or something that tells you when it's full?

Yeah, running a stud finder vertically is a solid trick for finding fire blocks. If you hit a horizontal stud midway up, you're stuck drilling more holes. Regarding the settling, the best way to tell if it's tight enugh is by tracking your bag count. Calculate the cubic footage of those cavities and check the manufacturer’s chart. If you haven't used enough bags by the time you're done, it's too loose. Another trick for those narrow gaps around windows is using a smaller diameter 'whip' hose on the end. It fits where the standard 2-inch stuff won't. Just watch your pressure so you don't blow the drywall off the studs if it gets clogged!

Since you’ve alredy got the bottoms open, pick up one of those cheap endoscope cameras that plugs into your phone. You can snake it up there to check for fire blocks or see if the cellulose is actualy reaching the corners. It saves a lot of guesswork. Also, just a heads up—blowing insulation thru an open bottom gap is going to be incredibly messy. You’ll want to tape some plastic sheeting over those openings and just leave a small hole for the hose, or you're going to have gray dust on everything you own.

Try the "thump test" as you go. Once you think a bay is full, give the drywall a firm knock with your knuckles every six inches or so. If it sounds hollow or rings, you've got a void that needs more material. A properly dense-packed bay shold give you a dull, solid thud. Also, to handle the mess at the bottom, I ussually staple a temporary cardboard flange around the opening. It keeps the cellulose from spraying back out at your face and directs the overflow into a bin. Just make sure your hose is marked with tape every foot so you know exactly how far up the wall you are.