Considering a purchase: My main concern is unit limit or population cap.

[Actaeon]

I've played strategy games since i was little, mainly Command and Conquer, and the Warhammer 40k games have also been brought up on a number of discussions. First, would Dawn of War 1 and its expansions be good for experiencing the "overarching lore" in detail?
Second, and my primary concern: How does the army limit work?
So, i've seen a number of skirmish games and it seems that they typically stop at 20 for infantry, 20 for vehicles, making the cap essentially 40, not including the supply cost higher tier units may require.
With this cap, how large do armies get REALLY? What factors into the army limit and how high can it really get? Just how does the cap work in general? The lowest population cap I've seen was in Halo Wars 1 and THAT felt like it was still bordering on being TOO limiting.
I've been interested in looking into the 40k universe and its lore to see what the "buzz" is all about, so the concerns I listed are the main things holding me back from getting this game.

[iKorv1n]

I wouldn't say that the Dawn of War games were specifically lore heavy but they nailed the vibe of 40k. If I'm to elaborate the story of all the campaigns deals each with their own contrived sideplot to the space drama happening at large with flavor sprinkled on top. I've only ever played the first Dawn of War and I'm mostly going off memory right now because I can't actually start my game. I just bought the base game and Steam is currently out of actual keys until the publisher sends more. So you can still pay, but can't play; essentially preordering for restock. Be that as it may, it only cost me $3, can't be too mad.

As for the restrictiveness of unit caps, I remember it feeling limited at times. Wanting more but not being able- but never lacking enough to overwhelm AI in campaign. I can't recall specifics on that note, sorry.

What I can comment on is that, obvious nostalgia aside, the first Dawn of War is one of the best RTS games I've ever played. It's old as hell now. It's graphically and technologically dated, though there is some modding you can do to fix resolution, zoom, etc.. Some of the voice acting is amazing, some of it was bad enough to become memes. If you do get it and don't end up personally enjoying it, I hope you can still see why it encouraged such fandom for the time it came out.

[Renfrew]

Each squad and vehicle has an assigned squad and vehicle cap value. For example space marines' scout squads have a squad cap of 1, so you could build 20 scout squads if you decided to build nothing but scouts. Commanders and some special units do not count towards squad cap.

This Dawn of War in particular you can get larger armies, in later games the squad cap for many units has been rebalanced and increased, as well as limits on how many of certain squads you can have.

If you want large full-scale battles then you should look towards Soulstorm and get the Ultimate Apocalypse mod.

[HighLanderPony]

You can have pretty big armies, especially as Eldar. It isn't Total War scale though. If you want more units there are always mods.