battleorder.org is a great place to start. this is another good place:
https://tmg110.tripod.com/usarmy_mcv.htmThings change a little as the war progresses so these answers are specifically from '43 onward.
I can fill in the blanks
Recon Troop- consists of an HQ section, Scout section and an Armored Car section
Scouts are infantry mounted in 6 Jeeps. 3 are armed with 30cal MGs and the other 3 carry light mortar teams
AC section is 3 M8 Greyhounds
HQ is 2 M8 Greyhounds and 2 Jeeps
Additionally Cav Recon Troops attached to Armored Divisions (ie Cavalry Groups) only have 3 Recon Platoons and 3 Assault Gun Platoons.
Armored Field Artillery Battalions are organized into 3 companies each with 6 SP 105mm guns (M7 priests).
FA Battalion (no Divisonal HQ section)
-3 companies of self-propelled 105mm guns
-each company has 3 batteries of 2 guns
Lastly US companies and battalions have HQ sections that are fully armed platoons (exception being artillery has no HQ, and Tank Destroyer Battalion HQ is Jeeps only). Armored companies and Battalions have 2 vehicles of the same type as their HQ.
Medium Tank Battalions also have Assault Gun Platoons with 6 Shermans (105s after July '44, standard 75s until then). On paper these are 3 tanks in Bat HQ and 1 added to each Company HQ, but in practice they kept them together as a single troop.
Last unit you need is an Division-level Armored Engineer Battalion. Its equipped the same as any other Armored Infantry but without the AT guns, instead they have a bridging unit. Their small arms are decidedly more close range with an abundance of M3 grease guns and just so, so many explosives.
For modelling at 3-5 vehicles per model you'll need 4 Halftracks on each Infantry Company. Standard issue was 20 Halftracks per company (2* for HQ, 5 for each Rifle Platoon, 3 for the AT platoon)
*the maintenance M3 was armed and fought a lot more than intended since they would perform battlefield maintenance and aid stuck vehicles, etc.