I dont know answers to all your questions, but from my experience it works kinda like you would expect from it in real life.
My first ever attempt to create deathmobile was a giant, electric long truck, all made from extra light frames except for two-row heavyduty frames bumper reinforced with two rows of military ceramic armour. Then i tried to ram some heavier enemies or move a motorbike out of the way.
Well, all the interiors were crushed badly, while bumper took little damage.
And i strongly sugest, screw the light frames. Sure, they weight less, but that only affects fuel/energy consumption. Power of engines in this game is strong enough that it isnt a problem to drive anything about 100 km/h, and you dont need more.
After about 200h put into the game, and many experiments, i belive all heavyduty frames vehicles are the best, and every outer piece reinforced with compund armour, double at the front.
My current most succesfull character has a 19t Mothership, 12 military wheels divided to 3 rows, 2 big electric engines, and 25 upgraded reinforced solarpanels. With 10 big storage batteries i can drive arround 2 days in a row and i takes about 5 sunny days to replenish. But you can allways add 3rd engine with generator and spend like 10l of disel to quickly power up if really need to.
PS. But remember it takes ton of time to weld, and even deconstruct heavy frames from other vehicles. It can take more than 60 full days of work, even more if youre unprepared (need to go hunt for food, cook water, dont have welding rig powered by big batterry etc. To not have problems with food early, i suggest going to swamp and collecting watercanes, with a little cooking skills you can make them into flour in few steps. One day and you can have like 300-400 flour. Then take one 200l barell, fill it with water, and cook it, or use water puryfining stuff. You should be set for building your dreammobile).
