Hi Colin,
Tha t is a very broad question.
What kind of models are you intending to make.
If you are making model engines, then BA and metric would be the best choice for Tap and Die sets however, it really depends on what you intend to make.
The Chester Conquest is a very capable machine for its size, that said, if your budget allows, I would recommend you look to a larger machine.
From past experience, I started with a Cobra 3 in 1 having been out of engineering for over 20 years and thinking, I would never build anything larger than the machine could handle.
I now have a 1.5 tonne turret mill and a lathe that can swing 13″ over the bed and 30″ between centres.
I got caught by the engineering bug and rekindled my apprentice roots.You never know where this hobby/passion will take you.
My advice is to evaluate what you want to achieve/build and then buy something that is capable of machining something 50% larger.
That way, you will never push your machine to its limits.
regards
CB