marines are supposed to be a 15% chance, if remining points > 500 as well , so very rare.
You have a lot of panzer 4 with the 75mm HE chucker (half your force). I concentrate on the P3 with decent 50 L/42 and then L60 when I can get them, and have not more than 1/3 of P4 for infantry CS. Probably just a section of 2, whose job is to acompany each leg rifle coy, and I generally prefer stugs for inf CS as the armour is usually better (embarrasing if they get a track hit though

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Panzer 2 I find worthless in any number. A section or 2 for recce, and as reserves in the defence (they have better armour than the GE armoured cars, which I really did not bother with, as and until the Puma arrives, then I replace any P2 with them).
Brandenbergers in the core is just, well silly

- these are "special farces" and were rarely seen, definately not a part of a line panzergrenadier coy!. Should really be limited to historical scenarios. Rather expensive.
A core arty battery will increase in experience - so should be bought at the start. Experienced batteries arrive faster, and perform CB fires more often.
An observer in the core (I always by mine just after the A0 so it is right there on page 1 of the units display, easy to find) will gain experience, hence will call arty quicker. Combined with experienced core arty, faster responses.
You have 15 sabot rounds with the P3s, and even the 50/L42 will execute matildas and valentines at 300M with this round, especialy if you engage halted, get above 80% to-hit and so some "special" hits. The L/60 will stretch that to 4-500M, and the plain AP round is good. Get into positions where the valentines are coming to you (over a ridge say) and wait till they show at 3-400m.. (use your arty and mortars to drop smoke, at a pinch your infantry, if necessary, or use battlefield smoke e.g. from wrecks).
Remeber that the germans used to try to coax enemy armour onto a Pak front. Some 50mmL60 ATG and also when available, the long captured soviet 57mm is good. (the 57 I have picked off valentines at 600M with ISTR). They can move a hex, unlike 88s and 75s so can adjust position slightly, but in the core a transport light truck is a useful side-kick. Get to an objective cluster and set up a pak front onto the approaches, preferably with a 3-500m fielsd of fire, some grunts out front to protect the Pak. Wait
You should have about 4-6 on board arty barrels in your core. use these to break up approaching infantry, drop on tanks to button them up (cannot spot as easily, get unhappy, and hitting is worse if supressed). The arty bursts will cause battlefield smoke at the point of contact, which your P3 can use to reduce the engagement range to the 250-350M sort of range they can deal with matildas at (and T34 etc). Even frontally. (Ignore any long range duels till you get the 75L43). Be prepared to stalk the beasties (e.g. round a hill or trees) to get the flank shots on valentines.
Also - use your on map arty, if thy have the range, to chop any AI on-map batteries. When you fire CB on a battery of 4 or so guns - use maximum effort, target all that reaches as a "hammer blow". NB - the 15cm Sig (with ammo supply units) - is a very effective CN tool. Also good for chewing up approach roads (e.g. on winter maps or wooden bridges over water).
Always take the P3 models with at least 5cm armour on both hull and turret front, preferably 6 and 7cm versions. Ensure you dont expose your flanks to 2-pounder. with 5 armour, you are reasonably safe v 2 pounder shot at 750M, with 6 definately rather safer.
Cheers
Andy