Personally i don't enjoy constantly upgrading equipment, machines, locomotives and wagons... so i made the changes to the vanilla items instead. If you prefer something more realistic and maybe balanced try Power Armor MK3, Storage Tank Mk2, Battle Locomotives and Battle Wagons instead.
Why 120 as inventory size and not 100 ?
Because 120 is divided by 2,3,4,5,6,8 .
100 is only divided by 2,4 and 5. Useful if you use mixed-ingredient wagons for crafting, else it makes no difference.
Why you didn't increase the train cargo wagon weight to match the new inventory sizes?
My though process is that a wagon is a 6x2 entity. Already 12 (6x2) unmoded steel chests could hold more items than a single wagon could. I believe that the vanilla cargo wagon inventory size is way too small anyway.
You had to increase the health of the vehicles ?
Well come on... i added grids so you can add shields and lasers... a 500-1500 health increase is nothing compared to that.