Welcome buddy!
Good choice! Are you aware of the small issues K series have? I currently have an MG ZR with the 1.4 K series in.
Cracking engines, and every one that I know who owns an F or a TF love them.
There are a few routes to take with the K series, depending on how much power you want.
If you buy the 1.8VVC model, you can get it ported, larger valves, Independent Throttle Bodies, piper 270 cams vernier pullies, forged pistons and rods and that should give you about 200BHP from the N/A motor.
A common conversion nowadays is the Kseries turbo. Either turbo the 1.4 (They have thicker liners, shorter rods and handle around 7psi of boost all on stock internals. This should give you, pared with a remap, about 150-160bhp on tap. However, more power will require stronger internals, head port matched to the VVC inlet, more aggressive cams etc etc
Another very common conversion is the 1.8 K series turbo. Which is found in the ZT or Rover 75. ZT tune, the engine is 160bhp and the 75 engine is around 150bhp. A simple remap will push them to 190bhp, and T25 or similar will get the power to around 220bhp. From there, you'll need forged internals, slightly lower C/R, more aggressive cams etc etc.
However,
Due to the space, fitting a turbo engine is difficult. Depends on your mechanical skills. Also, the turbo conversion into the TF/F you will need a exhaust manifold as it hits the sub frame.
