You are so right 😁
1. first of all, the generation from old to new: Series 9 -> Series 9 Pro -> Series 9 Pro+ (the latest version)
That's why the Series 9 Pro+ are usually more expensive than the older models, which are still on sale.
2. then choose the desired accessories: I would always want to have the cleaning station with me. Then decide on the soft case or the power case - depending on how much travelling you do. But remember: the razor itself will give you many shaves - depending on your beard growth, of course.
3. now you know which parts you want. It now remains to choose the best colour, although you can often save a lot of money with the second best colour
And don't forget, if you choose the cleaning station, to order a multipack of cleaning cartridges. They are far too expensive individually, but a multipack is a good deal.
(Tip: At 
https://www.braun.de/de-de... you will find a good overview of the common version combinations with the respective product number)