Depends how much a van costs, how much shit you want in your van and how good you are at DIY. I've seen people do builds for $100. A $1000 build in the back will get you some nice comforts without being over-the-top. You could drop $10,000 on a build and have showers, fridges, a big TV and remote-controlled pop-tops. You could spend $100k or more on a pimped-out RV.
Reality is, if you're doing it for travel/sightseeing or to chase seasonal work it'll be cheaper than paying for accommodation etc. If you're willing to sacrifice the creature comforts of renting your own room/apartment it can be WAY cheaper than renting in a city. >toilet
Gyms, public toilets, fast food joints, nature if you're /out/ or you can get cheap compact chem/composting toilets from Home Depot or a camping store. You could even just make an emergency shitter out of an old paint bucket w/ a sealable lid so you dont have to worry about late night or early morning shits. >showers/bathing
Gyms, hostels, beach showers, camping showers (canvas bags you hang from a tree or black PVC pipe on your roof with a nozzle fitted), or you have the rivers and lakes. Just depends on your climate. >cramped space
Even if you get a nice big van or RV you're gunna want to spend as much time out of your van as you can or you'll get cabin fever. This'll be hard to avoid if it rains for a few days/weeks but try to make use of cafes, libraries etc to study or do work at to just get out of the "house" for a while. >Where can I park?
Depends on your country, state, city. Campermate is one good app, there are others I can't remember right now. If you're in the US/Canada you have Walmart and BLM/Crown Land you can park freely at too.
Get a good cooler, make sure van has extraction fans, get a hammock or a tent to mix things up. Power/solar is nice but not needed unless you want to run a fridge or laptop.