Get the Lock Hacker once you get in the abandoned harbour buildings
Get a Metal Detector as soon as possible
Upgrade you tanks
Bounties are your main source of income until you get near the hell's gate where you might find a special rare enemy
MC has the best innate pilot skills so give him your best tank all the time
Mechanic isn't meant for battle on feet and he's super frail
Soldier Girl is actually the worse pilot so give her something with lots of ammo to make up for her low piloting skills, eventually she'll catch up
Golden Ants are a good source of extra income early on in the game and can be one shotted with a certain item and a few special weapon, I'll let you find out what's that item though.
Certain Bounty monsters will be forced encounters on feet, like OP's pic, be sure to have good equipment on you.
Protectors should be saved for the aforementioned Bounty monsters that you have to fight without tanks
If you find a certain route to be too hard just explore some more, the world is completely open once you destroy the two cannons.
The Tank Loan service isn't actually too bad, but be careful since your income will be halved as long as the service is active.
Mod your tanks often, it's better than buying new parts sometimes.
Explore some more
The plot is there but you need to explore to unravel it
ALWAYS have a repair kit or two with you
MC's dad can raise REPAIR skills by one on all characters each level up, it's pretty good to keep doing it for a while in the early game
Being a swell dude is fun, even though there's no reward besides people's gratitude
You can use weapons equipped on your character in the Buggy, which is a pretty good choice for the Soldier Girl early on
Rodriguez is VERY strong
Search for Traders camp, they're not explicitly visible on the map but certain trees give them out their camps
There are some VERY good parts in the world map AND dungeons, use your Metal Detector.