I'm using the Fortress Europe book, and am thinking the following based on what I have and what I want to build toward.
---600---
The base list with modified requirements (only 1 combat platoon required). It gets me some tanks, some armored Rifles, and some artillery. Seems like a good base... I think.
Armored Rifle Company
HQ w/ M3 37mm gun 40
Armored Rifle Platoon w / 2 Rifle Squads 240
Tank Platoon w/ 3x Shermans 205
Armored Mortar Platoon w/ 3x Mortar Sections & 2 50 cal
AA MGs 115
---1000---
At 1000 the relaxed limitations for the combat platoons are gone, so I have to add another Armored Rifle Platoon. To go with it, I'm adding another Sherman and a Pair of M8 Scott Armored Assault guns to support my infantry. The M8s seem like a good cross between mortars and light tanks with just a little less armor, but I have no idea if they are actually good.
Armored Rifle Company
HQ w/ M3 37mm gun & Jeep mounted
AA 45
Armored Rifle Platoon w / 2 Rifle Squads 240
Armored Rifle Platoon w / 2 Rifle Squads 240
Tank Platoon w/ 4x Shermans 275
2x M8 Scott
HMCs 80
Armored Mortar Platoon w/ 3x Mortar Sections & 3 50 cal
AA MGs 120
---1500----
At 1500 I add an Armored Anti-Tank platoon with Bazookas to help keep the Tanks at bay. I also add a unit of Priests to go with another Scott for some (hopefully) decent artillery support. Lastly I round it off with some limited air support because I like planes

I was also thinking that the air support could be swapped out for some 155mm artillery or another Sherman + a machine gun platoon or maybe some recon, but I just don't know. Any help here is appreciated!
Armored Rifle Company
HQ w/ M3 37mm gun & Jeep mounted
AA 45
Armored Rifle Platoon w / 2 Rifle Squads 240
Armored Rifle Platoon w / 2 Rifle Squads 240
Armored Anti-Tank Platoon w/ 3 Gun Sections and 3x Bazooka teams 135
Tank Platoon w/ 4x Shermans 275
3x M8 Scott
HMCs 120
Armored Mortar Platoon w/ 3x Mortar Sections & 3 50 cal
AA MGs 120
Armored Field Artillery Battery w/ 1 Gun Section 185
Limited Air Support 150
Thanks for looking and making it this far!