Yeah, I wouldn't care much if you decided that tracking ammo for the machineguns isn't worth it. If I remember right, they had boatloads of ammo anyways and typically were only consumed in large amount during advancing fire and the morning ammo expenditure roll. The exception was the .50cal AA MG, which only came with 6 boxes of ammo (compared to the 30+ of the Co-Ax). But overall tacking MG ammo and replacement periscopes (both optional rules from Patton's) is probably too much detail for too little gain. Main cannon/MG Malfunctions might be worth including though.
Advancing Fire being planned is good, its a very useful tool. I also agree with your idea to simplify it down to just a chance-to-kill on all enemies rather than Patton's method of selecting up to 6 zones with markers. Not sure if you want to emulate Patton's rule of advancing fire weakening as more friendly tanks get knocked out over the course of the day, but if so, you could simply model it as a penalty to the chance-to-kill roll for every 3 or so friendly tanks destroyed.
As for skills, intial thoughts without having played much is that the activation percentages might be a bit too low. Mostly the 3%/5%/7% ones feel a bit low but like I said, I haven't played much with them yet, so I could be wrong. The one that stands out to me is scrounger. Scrounger has decent odds 10/25/40% but at the same time I think to myself that I almost never have to resupply during most missions, so the idea of putting points in that for how much you get out of it feels like a waste. Once advancing fire comes in, though, that could change as I'd be expending a lot more HE shells. As a suggestion, maybe scrounger could instead give a bonus to sourcing more HCBI or HVAP shells each morning? (or a similar skill that does the same).
I admit I practically never use smoke rounds*, but the idea of potentially getting more HVAP rounds is pretty appealing if I'm in a 76L armed Sherman.
* I almost never use WP/HCBI smoke rounds because my two options are wasting a turn changing the gunload (Which is bad because I'm usually in a tight spot if I want smoke!) or firing a damaging shell at a target to clear the chamber and hope RoF kicks in to load the smoke round. This means the enemy unit will probably shoot back because I attacked it and I might not get my smoke if the RoF fails! Easier just to use the smoke mortar if present and, if not, just have the commander throw a smoke grenade and sit tight and hope the enemy is low on ammo and that I don't look worth the AP shell.
In a different topic, you put the campaign calender to an external, editable file. That is cool, looking at the format I think I understand it and I'm tempted to create a version that covers an alternate combat calender from an old Avalon Hill Magazine that features a Canadian Tank unit. However I think I'll wait for now as you might change the format at some point and I'm lazy about manual data entry.
To be honest, it looks like a "hard mode", I mean look at those activation percentages! It seems you'd see a lot more combat on average than the default US 4th Armored Division campaign. That said, they do get access to the Firefly with its 76LL gun, which is cool. I mean, who wouldn't want a tank that always starts a fight hull down and has a gun that basically fires HVAP as standard ammo, punching through anything short of a King Tiger or Panther's front hull armor with ease (and for those you get APDS rounds, which are super HVAP)? I mean, other than the Firefly having a special rule that replaces most of the "Enemy fires at lead tank" action results with "Enemy fires at you" because they're terrified of that 76LL gun and concentrate fire on Fireflies when IDed.
Of course, my big dream would be getting to drive the M18 Hellcat Tank Destroyer, the ultiamte in "High Risk, High Reward" Panther/Tiger killers. But, I'm rambling at this point, so I'll just shut up.
[edit] You don't get XP if you don't finish the day of combat? Ouch, teach me to throw a track an hour before sunset! I think it'd be fair for the surviving crew to still get XP, maybe apply a penalty though, like halving it.
