Dont let the price make your choice if you are into riding. Now if a bike is a good idea but you've not ridden in years maybe something smaller and less $$ will do until you ride seriously or find your niche.
There are quality folding bikes out there, but in general you’ll be compromising on wheel size. Storing a full size bike in a bag like @ducnut suggested is probably your best option. If you do choose to look into folding bikes then Dahon, Bike Friday, and Brompton would be the brands I’d look at.
Another benefit to a folding bike is if you’re in a metro area with nice bike paths you could do a longer ride and sightsee more and then get an Uber back to the truck instead of worrying about riding a loop to get back on your bike.
Yes those are easily done. I ve seen people using them next to truck before. Road bike people use them alot in winter or rain stops the skinny tire crowd.
Prolly noisey with knobbies but i have not tried it
I’ve used one. I got bored with it. But, it was good to nurse my knee, after surgery, because of its consistent resistance.
Technology of trainers has moved WAY forward, since I used one. Research “Zwift” and the silliness of the many hammerheads who participate in that. It’s possible to ride with world tour riders, as it’s real-time, interactive “social cycling”, for lack of term.