The answers to this are not really technical, but depend on what you plan for manufacturing, assembly and the logistics of that. Depending on the fab house, they charge for extras, so it may not work out cheaper.
Personally, I use a dirt cheap fab house, at 20$ for 10 boards its simply easier to order 3 separate boards. FR4 is quite tough on saw blades, though I recently bought a diamond saw.
At work we create a "mini-panel", we call it a biscuit (is that a standard term?), which is used for assembly. The biscuit sits on a carrier and travels through P&P, reflow, wave. After that it is split and the boards tested.
Anyway, it's a tradeoff between setup costs and unit cost, all depends on volume.