I wouldn’t worry about getting a mac and having problems acsessing drives. There is always a work around and they are free.
As for what mac to get, is your work mostly studio or location? If studio get a 27 imac, non retina. If you shoot location go for a loaded MBP and as mrsmith has said, a decent monitor for processing images at home.
The iMac screens are not perfect but if you know what you are doing (you can always go by the numbers) it’s propely calibrated and you keep the brightness at 50% they are fine. I work with one and when I see my work in print I don’t find myself having to review my work flow.
As for lightroom…have you tried capture one pro? We use P25’s, P30’s and IQ260’s so it makes sense but we also use 5d’s and which ever way we work capture one is fab. You can use pro on trial for 60 days. Capture one DB is free to use but will only work with thier backs.
Hope you find a solution, yes there is a perfect of way doing things but it is also very costly and being self employed that probably won’t be an option so do loads of research and find what works for you.