A few questions about mid and late game

Good afternoon gentlemen
As a new player with only a few online games, I obviously have a few questions about mid and late game. Until now I have rarely run into problems in the early game since I play very aggressively and usually dictate the game for the first 5-6 minutes. But this is when the problems start - when my opponent goes mass MG and mortar, I find it hard to deal with it! Now if they only defend with this strategy I can find a way around it since I retain the initiative and dictate the tempo. But when they start to slowly move forward and basically "squeeze me out" I tend to fail hard.
Attacking with infantry into 2 or 3 mortars plus MG is just not an option and even if you can flank the MG, most of the players are not sleeping and have at least one squad to delay you untill the mortars do their work. I tried building my own mortar emplacement but early game it seems to be more of a liability than an asset - it is rushed right away by everything plus a Luchs or a Puma and PIAT's don't seem to scare those at all! I also tried building an armoured car but by the time I got it my opponents already had a Pz4's /maybe I get it too late - what is the appropriate time for an armoured car?/. Also if I get an armoured car, do I delay my tanks way too much? From my experience even one unopposed tank can do a lot of damage.
So now I'm thinking a Bren carrier with the flamethrower upgrade to rush MG's from behind /that MG incendiary ammo is no joke at all!/ into fast Cromwell?
And one more question about the late game - how do you best attack a defended position - all out assault from two sides /if possible/ preceded by a heavy barrage or a slow grinding down with bombardment and a gradual advance? The latter seems to be a lot less dangerous and is bringing less casualties but it's sooooo slow and you have to fixate on it, leaving the other frontlines without much attention.
Thank you for your help in advance!

If you plan to get the AEC armored car, just rush it to maximize the impact. You usually should be able to get a Cromwell out -+2 minutes next to the P4 even if you build the AEC, and if not, the AEC should be vetted up and capable of snaring the P4 for AT guns, the important thing is that the vehicles are not unopposed. The way your infantry gets punished by vehicles practically makes you go the AEC anyway. PIATs work properly only against the big tanks, because they can actually hit them, so unless a heavy tank hits the field, the PIATs are mostly useless. UC is a great choice against OKW, because their light vehicles take longer to field and their Fausts require a building. Against Wehrmacht, you have to be very careful from the start, and after a 222 enters the field, the UC usually dies, so I am not sure if it is worth it against Wehrmacht. And yes, building a mortar pit is quite risky no matter the time. If you build it early, you risk it being rushed, if you build it later, you risk it being simply hard countered by a mortar or LeIG spam. Most of my good games and games that I have seen had the mortar pit in a defensive spot, slowly vetting up and bleeding the enemy. It is an emplacement, which means it naturally works better protecting your own territory than supporting an assault.

Thank you mediev!
In my last couple of games I just rushed out a Cromwell and it turned out ok. So I'm skipping armoured cars for now
Still undecided about the mortar emplacement though - sometimes it works, sometimes not, so I guess it's situational whether you build it or not.

i think replay would help us to point your main mistakes

Hi!
I'll try to put one up, but I'm going on vacation next week, so it may be a while...