Upgrading Resource Buildings

Hey everyone a little noob question here

I see that when I click into a resource building I have four possabilities for my level upgrades. My question, when you upgrade a building do you upgrade each one at the same level like have them all be at level 5, or do you upgrade one until a certain level then start on the next one? Also do you make sure that ALL of your buildings have the same upgrade levels?

Here is what I have so far
Stone Mine:
Lv 4, 4, 4, 4,

Cropland:
Lv. 5, 5, 4, 4

Iron Mine:
Lv 5, 3, 3, 3

Lumber Yard:
Lv 4, 3, 3, 3

Do you think I'm off to a decent start? Should I change up my resource upgrade strategy?
Thank you
Gimpyrks

I keep em all the same cuz they are all lvl 15 (to get lvl 16+ resources it costs coins) but when i was upgrading em i did them all equally as for a good start it looks like it basically just gotta keep upgrading and occupy oasis for extra resource production

I agree with nick! If you do it this way you get an even spread of resources and not loads of one and none of another!
Also do them all up to level 15 after that it costs too much to make it worth it!

Thank you very much