Or Do I need to buy both?

If you haven't played Settlers, I can recommend the 10th Anniversary.

There is a Balance Mod by the community which restores partially the Balance from the original Settlers 2.
https://www.moddb.com/games/the-settlers-ii-10th-anniversary/downloads/s2dng-k-rebalance-patch
It should be easier to master the economy. The AI also takes advantage of it.
There are a lot of maps to download from https://siedler-maps.de

All Settlers games are discounted by 50% every few weeks.
But if you want to play the original Settlers 2, I would recommend the S2 History Edition, or the GOG Version together with the "RTTR" Mod.

Thanks, I picked them both up since they were 50% off.

Does the first game still break if you have a 4GB video card or larger? (The Settlers)?

You mean the original Settlers 1 or Settlers 2?

I've never heard of this bug.

There was a review for the game mentioning if you had a video card over 2GB that it wouldn't let you set graphics up on anything other than the lowest setting...