IMHO, the lens to start with depends on what you shoot.
If you normally shoot with short tele, then get the 150 or 180.
If you normally shoot with a "normal" lens, then get the the 80.
If you normally shoot with a short wide lens, then get the 60.
BTW, the "standard" 3-lens kit is 50,80,150.
I personally was going to go 40,80,180 to get a wider spread.
- But the 40 was significantly more $$$ than the 50, enough to not cost justify the difference. Plus the 40 was larger and heavier than the 50.
- Similarly, the 180 was more $$$ than the 150, or maybe it was that I could find cheaper 150s than 180s.
So in the end, I ended up with the standard 50,80,150 kit.
Personally, I would keep your other film format cameras. You would probably loose $$$ in the sale of it.
Several years ago I bought a 500CM + A12 back + 80CF lens for less than I paid for my Nikon D70 in 2004. That felt both good (I could finally afford to buy a Hasselblad, in the past it used to be an "only in your dreams" camera) and bad (the used price of a fine camera had dropped so far down).
As others have also said, each camera system brings a different feel of operation to the table, and based on what you are shooting, one could be better than the other for that task.