there are some cases where you cant fit all the structures you want on a planet. for instance if you have a frontline Volcanic world and want to put refineries, trade ports, cap and frig factories and broadcast centers on it, you are not going to have enough space.
sometimes you just have to choose what you want where. For instance, Desert planets are really good for building massive shipyards (like, 5 frigs factories, 2 cap factories, trade ports and labs) while you will usually want to use all your logistics spots on Arctic and Volcanic worlds for Refineries.
If you play TEC (i think you said in your other post you do) then keep dead asteroids for boradcast centers and use a starbase with the appropriate upgrade (Starbases are in Entrenchment in case you do not already have it) to generate trade income and act as part of an optimum trade route.
With broadcast centers, place them at the extremities and the central worlds of your empire, as well as at any frontline chokepoints in your empire, so as to prevent a culture takeover.
With refineries, like i said, other than Ice and Volcanic worlds, you should put them next to Un-Colonisable Gravity Wells (UCGW's) like plasma storms, debris fields, asteroid belts etc with neutral extractors (the things that look like normal resource extractor asteroids on your nomal planets, except without the planet). Extractors have a refinery limit (planet based ones have a limit of 3 while neutral ones have a limit of 4 refineries). Because refinery ships can phase jump to collect resources in adjacent systems, you dont need to place refineries at every single world. you can often use one central world to refine the resources of many planets, and you can then use the freed up logistic slots on other planets to do other things.
as for tactical structures, in vanilla, hangars are definitly more useful than turrets, however in Entrenchment, mines, a large bank of turrets plus a starbase, a few hangars defending important aero-space plus a few repair bays will generally deter even the largest fleet long enough to send reinforcements.... or at least cause some major attrtition to the enemy. a pair of repair bays appear to be the community norm for increasing the survivability of a defending fleet.
with tac structures, its all about placement really. in vanilla, tac structures dont really do much. In Entrenchment they are something to think about, but in the end nothing will stop a large fleet, other than another large fleet.