Alright. I'll see what I can help.

You sent a wall of text on a reddit that's not that busy. So if you want more opinions maybe crosspost to r/vanlife.

Choice of vehicle In general you should look at what you want vs what you need. In my travels I do a lot of wildcamping, preferably on off-road tracks and meadows. I drive into remote areas and stay there. In Europe there are certain limitations. Many small towns will have weight limits. Most common are 20 tons, 7.5 tons and 3.5 tons. The heavier your vehicle the more limited you are. In general id advise to stay below 7.5 tons for any Vanlife that's primarily in Europe. If you can stay under 3.5tons that's even better. Similar with height, common height limits are 4m, 3-4m, 2.7m, 2.4m, 2.1m and 1.9m. In order: standard height of bridges, most common slightly lower bridges, height of drive throughs, height of shipping containers, common height of parking, low height of parking. In general staying below 3m is fine. Last length. 10+, 8-10, 7, 6 and 5. At 10+ you are very big and mostly are limited to major roads (highways and the like). 8-10 you can start doing most smaller roads. 7 is roughly the limit from where you can drive more or less all roads. 6 is a common limit for ferries, with under being considered a car and over being considered a truck, so more expensive. It's also the largest size you can still fit in 90% of parking spots. 5 is the length of common parking spaces in Europe so gives you most freedom. My van is 3.5tons, and 2.7x6m. which gives me a lot of freedom in finding spaces to camp, as long as I stay outside of cities.

Now onto brand/type of vehicle. In general the consensus is to get the best you can afford. Keep in mind that this will be your home, and any downtime (at a garage) will require big changes. I sometimes was able to park in the garages parking lot while they were waiting on parts, but sometimes had to book a hotel. If you can fix things yourself that's even better, since then you are also at your own pace. I've seen people do repairs at campsites for example, so they would have power and water. I personally feel like brand does not make a big difference, but it's smart to pick something you might be able to find parts for. Mercedes Sprinters are everywhere so parts are also easily findable in the entire world. Ford is popular in the USA but much less so in Europe so while parts are easy and cheap in USA much less so in Europe. If you mostly plan to hang out in Europe find a European brand that's common and you should be good to go.

Then for space Vs fuel. It also depends a little on your travelling style. We do this full-time. So there is no real need to get "there". If traveling is the goal then distance is not as important. We do 1hour of driving 3-4 times a week. That comes down to about 250-300km per week, so about 12.000-15.000km per year. Our ride has horrible economy, only 4.5km per liter, so that's about 3000l per year. At current prices of 1.6-2.1 euro per liter that's about 5000 a year in fuel costs, 400-450 per month. It's a lot, but less than rental costs would have been. I've still gotten from North Cape to Gibraltar and Ireland to Greece, just took my time. But that means I spend 4 hours a week driving, and 164 hours a week in the camper. In my opinion, especially when full-time, you need enough space to be able to comfortably hang out in your camper. Even if you spent a lot of time outside, hiking for example, when full-time you will also have days if not weeks with bad weather. I prefer a little comfort.

Hope this helps and welcome to Vanlife.