Apologies for not knowing, but I wanted to know if it was possible to play steam games off a external drive? I heard that it would need to be at least 7200 rpm and usb 3.0. Is it okay? and regardless whether or not it does, can anyone recommended one?
as already said, you will not have any performance issues playing your games from a modern USB 3.0 external drive as long as you make sure you are using a newer drive series.
Additionally, our own and independent research on current hard drive series do not show significant differences in drive reliability. Nowadays objectively all major hard drive manufacturers are working hard to optimize performance as well as reliability with each new generation of drives. If the right drive type is used in each scenario, modern hard drives usually last much longer than their minimum life time expectancy.
Therefore, RPM is not necessarily the only factor you should take into account. In regards to performance and lifetime expectancy, you should consider the main purpose of your new drive(s). Since you mentioned gaming and are looking for performance, we would recommend a modern BarraCuda or -even better- a BarraCuda Pro (whereas for example in a NAS environment which is usually operating 24/7, you should use specific NAS hard drive(s))
Yes, you will manage to play games off your external hard drive with no loss of gameplay quality (except for potentially longer loading times, but that's just a small price to pay), provided you are willing to carry an extra box around if you travel.
Most general-purpose external hard drives are 2.5", which is what you are probably used to. For a proper hard drive to play games with, you'll definitely want a 7200rpm one, which (as far as I know) only 3.5" drives are capable of. These are a bit heavier and bulkier, hence why I mentioned the extra box.
I would recommend the Seagate Expansion 2TB (3.5" version). Although I have never used it personally, it has great reviews and appears to be the most popular one as well.
Just be aware that does not mean you can simply install games to the external hard drive and then attached it to any gaming PC to play the games. You can only play games on your PC where you installed the games to.