From the ground up. I'm going to start with an infantry platoon and company:

INFANTRY COMPANY, 161 personnel
** HQ SECTION, 19 personnel
*** Company OC - Captain - Rifle, Pistol
*** Company XO - Lieutenant - Rifle, Pistol
*** CSM - Sergeant-Major - Rifle, Pistol
*** Quartermaster - Sergeant - SMG, Pistol
*** Signals - Sergeant/Corporal - Rifle, Pistol
*** Demolition - Sergeant/Corporal - Rifle, Pistol
*** Medic - Sergeant/Corporal - Pistol
*** Clerk - Corporal - Rifle, Pistol
*** Mess Sergeant - Sergeant - Rifle, Pistol
*** Cook - Corporal - Rifle, Pistol
*** Cook - Private - Rifle
*** Cook - Private - Rifle, UGL
*** Cook - Private - Shotgun
*** Bugler - Private - SMG, Bugle
*** Storeman - Private - Rifle
*** Orderly - Corporal - SMG
*** Orderly - Private - SMG
*** Orderly - Private - Shotgun
*** Mechanic - Private - Rifle

* SUPPORT PLATOON, 34 personnel
** HQ SECTION, 4 personnel
*** Platoon OC - Lieutenant - Rifle, Pistol
*** Platoon Sergeant - Rifle, Pistol
*** Radioman - Corporal/Private - Rifle, Pistol
*** Medic - Corporal/Private - Pistol
** HEAVY MACHINE-GUN SQUAD, 4 personnel
*** Gunner/Gun Commander - Corporal - SMG, HMG
*** Loader - Private - SMG
*** Spotter - Private - Rifle
*** Bearer - Private - Rifle
** LIGHT MACHINE-GUN SQUAD, 4 personnel
*** Gunner/Squad Leader - Corporal - GPMG, Pistol
*** Spotter - Private - Rifle
*** Gunner - Private - GPMG, Pistol
*** Spotter - Private - Rifle
** MORTAR SQUAD (x3), 4 personnel
*** Squad Leader/Gunner - Sergeant/Corporal - SMG, 60mm Mortar
*** Gunner/Loader - Private - Rifle
*** Bearer - Private - Rifle
*** Bearer - Private - Rifle
** RPG SQUAD - 6 personnel
*** Rocket Grenadier/Squad Leader - Corporal - SMG, RPG
*** Loader - Private - Rifle
*** Rocket Grenadier - Private - SMG, RPG
*** Loader - Private - Rifle
*** Rocket Grenadier - Private - SMG, RPG
*** Loader - Private - Rifle
** SNIPER SQUAD - 4 personnel
*** Sniper/Squad Leader - Corporal - DMR, Pistol
*** Sniper - Private - DMR, Pistol
*** Sniper - Private - AMR, Pistol
*** Spotter - Private - Rifle

* INFANTRY PLATOON (x3), 36 personnel
** HQ SECTION, 6 personnel
*** Platoon OC - Lieutenant - Rifle, Pistol
*** Platoon Sergeant - Rifle, Pistol
*** Radioman - Corporal/Private - Rifle, Pistol
*** Medic - Corporal/Private - Pistol
*** Platoon Sniper - Corporal/Private - DMR, Pistol
*** Platoon Sniper - Private - DMR, Pistol
** INFANTRY SECTION (x3), 10 personnel
*** INFANTRY SQUAD, 5 personnel
**** Section, Squad Leader - Sergeant/Corporal - Rifle, Pistol
**** Gunner - Private - GPMG, Pistol
**** Pointman - Private - Shotgun
**** Grenadier - Private - Rifle, UGL
**** Rifleman - Private - Rifle, RPG
*** INFANTRY SQUAD, 5 personnel
**** Squad Leader - Corporal - Rifle, Pistol
**** Gunner - Private - GPMG, Pistol
**** Pointman - Private - Shotgun
**** Grenadier - Private - Rifle, UGL
**** Rifleman - Private - Rifle/shotgun

This is half from WW2 so I need advice.

What nation's structure are you basing this on?

I mean my battalion TOE was based on the late WW2 British structure, all the admin staff was in the HQ company with stuff like mortars in a Support company. Hell feel free to steal my TOE.

I took a good note of what bayonetstrength had to say about British, Australian, NZ, US Army, USMC, German Grenadier, German, US and British Airborne, although most is probably stolen from commonwealth structures.

Mixed with what I remember of more modern things (not so much actual sources, I lost most of my pdfs), and a very small part of it is original.

Also up'd slightly, added support platoon and some more people.

Yeah, I used Bayonet Strength and chiefly the Commonwealth tables to do mine.

Though all the admin and support stuff was at the battalion rather than company level.

Something different now. I'm fleshing out armoured units. Some time in the 40s in Ekraysia, armoured and mechanised divisions, due to their square nature, were scrapped as redundant and all consolidated into new mechanised divisions of two tank and two infantry regiments each. Some time in the 50s the doctrine will have been carried down to regiment level, and all armour/mech regiments replaced with mechanised regiments with one tank and two mechanised battalions each.

Currently the doctrine will have evolved to have one tank battalion, one mechanised battalion in heavy APCs/IFVs to directly support the armour and one mechanised battalion in wheeled APCs to fight dismounted and/or on the flanks, like the Soviet BMP/BTR mix.

The HAPCs each carry a 25mm cannon, 60mm mortar and ATGMs so act as general support for the tanks. Can carry 10 dismounts.

So this is what I'm generally thinking:
Tank Battalion, 50 tanks, 6 HAPC, 302 men
*Bn HQ/support company
**Bn CO's tank
**Bn XO's tank
**4x HAPC: Admin (etc.) sections - additionally provides mortar and ATGM support for battalion
*Service company - exists, few armoured vehicles: 2x HAPC (ambulance, maintenance)
*Tank Company, 16 tanks (x3)
**Tank Platoon, 4 tanks (x4)

Mechanised Battalion (x2, 1 with HAPC/IFV, 1 with APC), 780 men each, 59 APCs/IFVs each
*Bn HQ/support company/
**4x APC: Admin (etc.) sections
**4x APC (119mm mortar)
**4x APC (Scout platoon)
*Service company, 2x APC (ambulance, maintenance)
*Rifle Company (x3), 4x APC (one carries extra missiles, repair stuff)