As a rule, never stock ressources you can't defend.
And to know whether or not you can defend it, then compare you forces to your 100+ closest neighbours.
If there are more than 5 players whose individual forces outnumbers yours by 3 to 1, then you suck in defense. they'll just use you as a golden kettle
looking to box a prov before saving for fort 6 is usually a good strategy, but I never box a prov in plain .... better still, playing a low point strategy with no colonization until 1000 pts inthat case.
usually in vers 4 or long-realms vers 3, you'll develop colonization and fort levels in lockstep :
fort 3 on your prov 8
if lucky, you'll colonize a close mountain prov (if not close, then it'll take longer, but that's it)
fort 3 or better, fort 4, in your mountain prov
boxing the mountain prov (3 to 4 colonization), with likely upgrade to fort 5 in mountain prov in-between
fort 3 for secondary provinces (for easy prod bonus), but no more
once the mountain province is boxed, you'll do a lot more researches to bring down the construction costs for fort 6 (university, architecture, military architecture) if you are in military mode, but also the costs of producting/gathering those ressources (bureaucracy, commerce) if you are in economy mode
In any case, you shouldn't have more than 7k-8k points when you start fort 6 and still have a very decent defensive army ...
But well, that is if you play defensive.
Perso, I prefer to stay on the offense as a mean to both gather the needed ressources and deny any cheap greedy ideas to my most immediate neighbours ...
