Mountain Pass

We have one tent, Eureka 3 season but the winner is the enclosed shelter or screen house. We spent 4 nights last winter up north with snow and the shelter kept us warm during the day. Of course we used the Buddy heater. In the tent however we were cold, sleeping bags to 15F and lots of layers we ended up covering the tent with a large tarp and it helped. I think tents are important but more so the screen room with walls.

People math and tents get hard. I'd always lean towards one person extra, so a 4p tent. There aren't a lot of light options in 4p tents though. We used a Eureka 4p tent for years, that weighed 8 lbs, and tried several times to find an alternative but never found anything worth it. At the actual 3p level, we have a Nemo Dagger Osmo 3p, that is pretty amazing, but we've only ever used it for 2 people. It's also very expensive, and doesn't seem to go on sale very often.

I’ve got two Eureka’s (2 and 4 person). The two is from 1995. No issues with either

For solo hiking, weight can be really noticeable after the miles. But it depends on what you consider affordable. For years I had a Eueka 4 person tent that was nice and spacious, but was just over 6 lbs. Adding a tarp as a sort of footprint was an extra pound. I just bought a NEMO ultra light that weighs 3 lbs. Doesn't sound like that big a difference, but I'm trying to get my pack from 30 lbs down to 25 or under in order save my poor shoulders on my next hike.

I was going to suggest eureka but they stopped production last year. My first backpacking tent. Very affordable, weight was fine split between 2 people. And my goodness, it lasted waterproof and zippers a very long time. Like most, I have bought and resold a few tents over the years but the eureka one remained in my loaner gear through it all. If you see a 2 person eureka, used, for a very low price, grab it and try it out for your first couple of trips

It depends on if you want to sleep closely to them. I would buy the tent I want for solo, then a cheap second tent just for the friend. I actually kept my first backpacking tent, a eureka!, just for friends.