I think any star system that contains 3 planets that have 125% rating and below would be great. Any bonuses on top of that would be fantastic. Try to keep the star within say 10 light years of the core worlds, so that accessibility score and travel time to the core worlds would be good.
Note: You DON’T need to start with Agriculture and “move” up the supply chain. Your colonies will “source” for input material from other factions.
Edit: The reason for having 3 planets in 1 system is that your patrol fleets will basically decimate any opposition that comes in when you have 3 patrol generating bases upgraded. And defending 3 with your fleet multiplies your effectiveness with travel time etc.