MESA board recommendations for 7 axis

Option 1
Use a PC with parallel port and add another addon PCI to parallel port
Or
A newish PC with 2 of PCI-E to parallel cards (some have 2 ports on one card so only one needed), but do bare in mind some PCI-E do software emulation so do not work at all for machine control.
This gets you 24 outputs and 10 inputs total, you need 14 just for the drives.
-you can do it with a single port if you wire 2 drives of the same axis together, only 5 inputs though.
Option 2
Mesa 7i92T has 2 ports with 34 pins total but each pin can be input or output or whatever needed, much, much faster step rates compared to parallel port.
- both above options will work with or without a BOB, BOB makes wiring easier but some can limit step rates even for parallel port.
Option 3
Mesa 7i96S and 7i85S gives you 9 totally independent stepgens, 11 inputs and 6 outputs ( i think), and full spindle VFD control with encoder feedback if you do end up needing it.
This can be wastly extended with Smart Serial cards, like 7i84 with 32 inputs and 16 outputs, 7i70 with 48 inputs, 7i71 with 48 outputs, etc.

No.
Wiring is tricky though, if you do not use BOB's, and very sensitive to miss wiring or overvoltage.
If you go with 7i92T, you can at any time add a 7i76 or 2 of 7i85S.
In short, Mesa are very versatile and easy to extend capabilities.
Having said that, i use bare 7i92 on plasma cutting machines with no BOB, directly wired to drives and "arduino" relays, never had any issues, despite plasma being extremely "noisy" and causing huge amounts of interference. This does require having some knowledge of proper wiring and grounding/shielding.