Probably the cheapest solution is the Mariner 4 your looking at $500 to take the whole family out and lakes, mild rivers, even light whitewater will all be doable.
The twain knockoff is made by aqua extreme it's the x2 tandem you'd be looking at $1000 for 2 boats but with more kayak like abilities and shallow draft, good stability etc. Rolls down to the size of a small sleeping bag so very portable and it is a better river boat.
Yeah, depending on construction methods its not always stocked in stores. In Greece I couldn't find anything at all especially on the islands. (Fortunately, I had my repair kit I brought with me).
In some areas where tyvek tape is hard or impossible to find I've seen other brands marketed as barricade tape, seam tape, or construction sheathing tape. Most of those are pretty similar to tyvek tape and bond to almost anything.
For longer trips or for those who live where it isn't available, ebay and amazon are amazing. I have a buddy who lives in South America and he has me ship him some packraft goodies a couple times a year.
A few months ago I had a rock tear a three inch gash in my raft, but I had drybags inside my tube so even though I lost pressure I was still floating and was able to get to an eddy. I tore off a section of aquaseal tape that I carry in my pfd contact sealed it to the tear. Lasted til I could get to a calmer section of river about 600 feet downstream, and I was able to do a full patch before finishing the run.
The biggest issue with that repair wasn't getting the patch to stick but in cleaning the inside of my tubes of sand after I got home. I was shocked how much sand got everywhere inside.
100% you want a kayak style paddle.
At the weight you are targeting, there really aren't a lot of options. The supai paddle is basically the lightest in class, so if that's where the weight target is, there's really just one primary option. That said, Alpacka sells a 15-ounce Ninja paddle that is basically identical to the Supai paddle (to the point I wonder if they source from the same factory). Cost is also basically the same, but Alpacka may have stock when Supai does not.
If price is a factor to the point you're willing to compromise on weight/dimensions, the Advanced Elements paddle is a common choice for beginners building a flatwater kit. Its 8 ounces heavier and a little longer when broken down, but only $50:
https://smile.amazon.com/ADVANCED-ELEMENTS-Ultralite-Kayak-Paddle/dp/B00YFPS7OC/
Honestly, I bought some thick gloves and didn't like how I couldn't feel the paddle. So I ditched the gloves and got some pogies. The pogies are undeniably warmer (like little pockets of warmth for your hands) which is probably do to the fact that they aren't snug against your skin. But they are really bulky to pack. All of the trips I've been on that required hand insulation were car accessed and I haven't needed hand insulation for any of the hike in trips that I've done. If I was hiking and needed hand insulation, I would get some 3mm gloves like these https://www.amazon.com/NRS-Maxim-3mm-Neoprene-Gloves/dp/B07N28DKYD
I just use something like this and rinse it off before drying and returning home. You can do that at the shoreline. Use a nice chamois to dry the boat.
no need to try and do all the cleaning at the house/apartment.
Are you sure you need a packraft? I've never used a packraft, but I kayak and did some whitewater with someone who was using a packraft. In order to be light enough to hike with, packrafts make tradeoffs on performance and cost. If you already do a lot of hiking, that might make sense for you.
But if your main goal is to do whitewater, you might have a better time starting in a kayak that isn't optimized for hiking. I'd start by finding somewhere you can take a beginners whitewater kayak lesson. The skills will transfer to packrafts if you decide that's wht route you want to take. If there's flatwater nearby you can get a cheapie inflatable to just get some practice.
December trips are cold as F. Get her a USB chargable hand warmer. Its like a hot water bottle but runs off power at the push of a button. Like this one:
She will appreciate it. I'm assuming she already has a battery bank/solar charger.
One area where you often see creative DIY options are items that are regulation-required for multi-day permit river trips, and that aren't common items for backpackers. E.g. like firepans or groovers.
Packrafters will push turkey basting pans or cakepans into service as firepans because they're light. Though the turkey basting pans are starting to be banned by Canyonlands and the San Juan River. An option that was as light and compact as humanly possible while still meeting the requirements of major river regulations would be useful.
Most river regs require hard sided containers for groovers, so packrafters will carry solid waste bags and then put them inside canyon kegs or repurposed nut jars from costco to meet the hard sided requirement. I recently tried out a commercial option on the San Juan https://smile.amazon.com/Lightweight-Affordable-Portable-Campers-Backpackers/dp/B089KXQVTW/ and this was nice because the container is designed to fit in a packraft tube. But its the first commercial option I've ever come across.
also when the regs require extra paddles or PFDs, packrafters sometimes get creative. I've seen people carry hand paddles (designed for swimming) as well as inflatable PFDs that definitely AREN'T Class III. Again, light and compact options that are still functional would be very useful.