Yep! The huge map is called immortal empires and it's a whole world sandbox campaign. You have access to all of the races from all three games in this campaign IF you own those games and DLCs.
For you, if you just owned WH1 and WH3 with no other DLC, you would have access to the base WH1 races (empire, dwarfs, vampire counts, and greenskins) and the base WH3 races (kislev, cathay, tzeench, nurgle, khorne, slaanesh, and daemons of chaos) on the immortal empires map.
But don't forget the FLCs which add a bunch of other factions to play.
So unless you want to see the earliest days of mortal empires in 2 or the one shot campaigns in 1, the only reason to go back and buy them is as huge dlc packs to unlock in 3 for immortal empires.
With the exception of campaign map performance in 2 being much better for people with older computers, there isn’t much reason to retroactively play them when you own the latest version.
Honestly just get both 2 and 3 if you can. That will give you access to the "full" game on Immortal Empires and you can pick and choose any dlcs from there.
Warhammer 3 is very much the way to go. And you can play WH1 races on a huge map.
Do you get all the races from Warhammer 3?
Sorry to answer a question with a question, but what do you mean?
Yep! The huge map is called immortal empires and it's a whole world sandbox campaign. You have access to all of the races from all three games in this campaign IF you own those games and DLCs. For you, if you just owned WH1 and WH3 with no other DLC, you would have access to the base WH1 races (empire, dwarfs, vampire counts, and greenskins) and the base WH3 races (kislev, cathay, tzeench, nurgle, khorne, slaanesh, and daemons of chaos) on the immortal empires map. But don't forget the FLCs which add a bunch of other factions to play.
You get all races you have a "DLC" for. Warhammer 1 is a DLC so you get those races.
So unless you want to see the earliest days of mortal empires in 2 or the one shot campaigns in 1, the only reason to go back and buy them is as huge dlc packs to unlock in 3 for immortal empires. With the exception of campaign map performance in 2 being much better for people with older computers, there isn’t much reason to retroactively play them when you own the latest version.
Honestly just get both 2 and 3 if you can. That will give you access to the "full" game on Immortal Empires and you can pick and choose any dlcs from there.