I want to use them as main infantry to replace conscripts in between early and mid game.First of all, I must point out the most obvious mistake right there. Trying to use them as frontline infantry. Guards riflemen are not supposed to be used like that in the first place due to the fact that they have high reinforcement costs and if you lose plenty of models in the field, you will be bleeding manpower like a stuffed pig. Just like the USF had a problem with their manpower bleeding before some patch saved their entire faction...
I know this is wrong, but any other use seems so bad compared with other tools soviet have.
I understand it's no use to spawn more than one guard.
Guards are meant to be used alongside conscripts to deter light vehicles and finish them off when they're at their critical part of their health thanks to anti-tank guns or anti-tank grenades.
Besides, if you use them as mainline infantry, who is going to act as your meatshields against snipers, MGs, anti-infantry light vehicles? It's just that you are not using them right.
They're meant to be used alongside conscripts due to their anti-tank snares and especially ZIS guns since their button ability allows the anti-tank guns to get a few shots off before the targeted vehicles/tanks get away. Now the Ostheer and the OKW may have their blitzkrieg abilities to get them out of the area and break out of the button's ability, but that is what conscripts are for. To deny such vehicles a possible way out.
Although Guards are categorized as 'elite' infantry, they're just infantry with better equipment and stats than regular frontline units like conscripts or penals at the cost of high reinforcement rates. I do think their munition abilities could get some decrease in cost, but other than that matter they're quite good for their cost.