You should always use and arm your Riflemen and Combat Officers first.
Disagree. Rifles are decent enough without bars, putting one or 2 bars on your starting RE squad gives you one extra combat capable squad on the field in the early game.
It's really a problem with basic faction design that can't really be helped. In VCoH it was helped by having the ultra light vehicles for scouting and anti-sniper, coh2 doesn't really have an equivalent.
The puma is a completely reasonable and balanced unit. It's a light vehicle killer; if you don't want to fight the puma don't go light vehicles. There is really no hardcounter to the t-70 right now unless they hit a teller mine. You are pretty much never going to get 3 pak shots off on a t-70 unless the opponent completely fucks up.
Command p4 needs to be put in t3. That's all the doctrine needs.
Change sticky selection in the options menu, it helps preventing the accidental retreats. What sticky selection does it leaves you on the last unit you had selected if you left click nothing. Since left click doesn't do anything except select other units, it's pretty much never an issue. If you turn sticky selection off when you mess up selecting a unit it wont leave your last unit selected to be retreated.