There are discussions on different forums about how good in terms of TPS (transaction per second) Stellar can be.
If I would like to achieve higher TPS, is hardware likely to be the only bottleneck?
It's not necessarily limited by one entity's hardware. There is a limit due to hardware, though. If nodes critical for reaching consensus are slower when consensus is achieved and the network progresses to the next ledger the slower hardware will be catching up.
A limit of TPS is also decided by validators as they upgrade their hardware. It is documented in a few places, for example under "upgrades" in our docs - look for maxtxsize.