Thats really up to you, as each setup differs quite a bit in cost. In an ideal world, one would get all 4 boards with heatsinks and 320H drivers. That way, you can run them soft or hard! Pretty much from 0 to 1400 watts. You can also get 4 boards with 2 600H drivers to save some money but will lose some flexibility with dimming.
I'll be adding the Meijiu 950mm long Osram red bars to my setup. Gonna make them mimick the HLG35 diode placement for Emerson effect. Each of their bars cost $60++. Its plug and play. I plan to place 3x800 boards side by side with one of those red bars between each 800 board.
Like below:
800 Board 3000K
Red Bar
800Board 4000K
Red Bar
800 Board 3000K
Space is 5×3.5 or so. Plants would FRY if I max out all boards. I'll have to play around to get the hang of it. Its really just for your reference. I've not done a single grow or completed the above mentioned setup. It is scheduled to be completed by mid April when i start growing again but should be done within a month. Hope this helps!
I think I will go with this idea of yours. Should be able to order everything by end of the week and then hopefully finish my current grow with it.