I love it but against Mechanized with the Stug E I tend to keep armored Slotted to smack the Stug E like the little bitch it is. M15 delays this.
When you build the lieutenant you should always unlock zooks couple of minutes later. If you go M20, always replace its crew with a RE one so you have a zook squad. Now I know stugE can easily kill any of your squads, that's a risk to asses every time.
It is really map dependent but going 2 or 3 RE can make you overwhelming him. Use the RE as scouting and capping squad and building holder while you use your rifles to flank.
2 or 3 RE start let you go easily to any commanders. its a trade-off for pushing power to capping power.
2 RE start with a bunker in a strategic location to hold until you get enough force to push.
3 RE start, no bunker but building holder in a strategic position.
4 RE start to Rifle commander performs well on many maps. It is really effective in term of manpower management but I wouldn't do 4 RE start with any other commander.
Remember that Ostheer need to keep his pio near to his MG to keep it effective, which mean for him less capping power or to replace a grenadier squad by a pio one.
Cons: more than 2 RE start make you really vulnerable to Grenadier spam. (just talking about early game)