5-15k atk+def
50-150k hull+shield
base module reference:
http://galaxylegion.com/wiki/index.php/BasesMost lv 4 aren't GP bases so probably only 40-50 areas or so. And probably very few clamps on it so calculating modules alone will get u a good idea. Note that although rank 4 base can build the 2nd to best tier of structures, most probably still run weaker ones(although won't be by much, the 5th tier being most common with some 4th tiers probably) so~
But there are strong ones and weak ones, so u might wanna start trying each one of them and make a chart of the strength of each bases. In the long run, you will be fighting the weakest ones of those(if you can afford the badges) so it will be quite a bit below average strength(there are semi-naked ones).