Downloading PC games to external harddrive

Alright guys, this is my first time posting on this forum site so I apologize in advance if I do anything wrong. But here's my question, I am buying a Dell XPS 13 and I plan to get Battlefield 5, lords of the fallen, war frame and league of legends on it but I have a feeling that I'll need an external harddrive and I don't know squat about them. I have been reading online that I need to be careful which one I purchase because some of them will lower your performance speed and as all gamers know, that is NOT and option. I also don't really know how much storage space I will need. I will probably be getting more games in the future so I want to leave a little leeway but will 1T be enough space? TIA for any help.

Without knowing any specs on your new rig, I can say 1tb should be just fine.

Personally I play Skyrim and Wow which are both very large games to begin with and theyre both heavily modded.

I also play L4D/L4D2 and Counter Strike which are all moderately modded.

Ontop of that I have around 30 other games installed and quite a few movies and I'm only using a 512 gb ssd with room to spare.

But as far as quality of performance goes I really can't be of much help, I've pretty much exclusively gamed from internals.