The First Minute

The tank is quite vulnerable near the start, he has a lot less health, no charge 3 or his product grenade.

What I do is farm money fast with my rail gun. It doesen't give much juice but if you can get money faster than the enemy team you should be able to easily force them away from your lane. Upgrade charge to 3 as soon as possible, this is your main killing tool and any enemy that dares to mess with your bots should be greeted with a charge. I usually upgrade health only when I need the quick heal and product grenade is something I buy a lot later.

I always like to have my deploy lvl2 as tank, for that awesome healing ability

I upgrade charge only, then run to the nearest creep wave. I try to melee if possible. 2 full waves of melee gives you 70%-100% juice, depending on how lucky you are with juice box drops. Go for charge ringouts if possible, as those give huge money. Run away from any gunners/assaults that are on you, unless you are darn sure they aren't running armor. If no armor, charge/spin to kill.
I upgrade charge 3 asap, and only do my passive if i need it to live. Optimal skill buying for me on my tank is:
-Charge 2
-Charge 3
-Passive 2/Grenade 2
-Grenade 2/Passive 2
-Grenade 3
-Passive 3

Insert Deploy 2 anywhere in that mix if you desperately need to heal quickly.