I send the Kret out to immediatly start capping, whislt I build a Logistiks then build about 4 more Pgrens, 2 G43s when I can. I then upgrade them using Extra Squad Size and move on to Kampf. You should build Kampf if you are unsure of what your enemy is doing because you can just upgrade to Shrecks (Provided you get the upgrade)
The main reason you want to go T1 first is because the units do not cost a lot of fuel, which T2 does.
Scout cars are not very powerful but are good for lockdowns, depending on how well I am doing I might buy one to lock down that +16 fuel for a fast tech. The cool thing about that is if you keep your car alive later you can just move it to lock down an ammo when you need more ammo for income. If it vets, always go defensive, it'll normally just be sitting at a spare sector. To me the other T1 units aren't very effective as Defensive Operations essentially fulfills the role of a Muni HT if you upgrade a foward barracks. The Vampire is defenseless but could be useful if you know how to use it well.
If you are seeing BARs or primarily infantry then I skip T2 (but ALWAYS go back to rebuild it, you need shreck upgrade for panthers) and go PanzerJager for some MP44s (They come without an upgrade :D) and some ACs. Normally I get a Marder III too, just in case.
(Remember when it comes to T3 it's either 360 MP or 75 ammo on regular Pgrens for MP44. I always like the options that PE gives when it comes to squad upgrades)
T4 is completely optional to me, I only build it if I want panthers. ATHT's are nice to clean up Marder Massacres. They work good in teams too, You break the treads and then a marder cleans up.
Panzer IVs are OK, good against inf and emplacements and nice to have but worthless against tanks. In Rapidfire mode these babys own rangers...if you have armor skirts that is.
"Balancers are 10 a penny"