Yes, if you want units then go for the most southern provinces first. The most norhtern ones and celtiberia need regionals. The only thing I can say is that the Lusotannan provinces and the most southern ones are good for recruitment. Tough you might want to build a level 5 mic in Asturia and Cantabria when you've a lot money. There's a nice surprise over there.

Here's a map which shows the number of recruitables in the native MIC there are in every province. How greener how more units. The more it is red the few. If it is grey there are none. However certain units may require a high mic level.