I think the OT is the best choice to start with, although you could start sequencing other gear with the monomachine too.

The AR cannot function as a hub. With the OT you’d have sampling covered and midi sequencing. You can use the OT as x0x drumcomputer quite nicely.
OT and monomachine is already a very powerful combination.

If you’d like to add more, get something with a shitload of knobs. The virus has knobs, but something like a nord rack (2, 3, 4, a1) has a more dedicated interface. In a live situation, every second counts, and having to menu-dive is not an option. The nord also has 4 part multitimbrality, meaning you can play/sequence 4 polyphonic midi channels from the OT. But I think it is wise to keep it as small as possible in a live rig, reducing the chance of problems with connecting and playing the devices