This question comes up all the time, so scour the archives. Start with some of the posts in this section of the forum. This process should take time and research, so do your due diligence and acclimate yourself to the forum. There is some very sage advice here.
Im a big believer in used, so if you are interested in taking some time to build a rig piece by piece, have at it. You will learn a lot. That being said, for the lighter weight range you may not be able to build up so much, maybe purchasing off the shelf or a used Tiffen will work well. Hard to say what is "better"
Remember that you should budget for follow focus, wireless, etc. but you can rent those and then purchase over time, or maybe you already have with your other gimbal systems.
There are Tiffen dealers in the UK
Optical Support is the group that I hear about often