unless you play on the smaller maps that shouldn't usually be an issue. that said, you should always concider how exposed a planet is when you decide what to do with it. maybe that size 5 is a good place to put a wonder, but if it is on your border you prob wouldnt want to put something there that would criple you if you lost it. also keep in mind you can always adjust a planet later.
personally, my base planet build is a eco planet. i put 2 factorys on every planet and a starbase, the starbase often gets built over mid to late game tho. most wonders go on the 8 and under planets. i build very, very few industrial planets. usually only when i luck into a starship bonus. this is because i try to control the pace of the game so i can take my time building up my military. if your style is brute force tho that obviously is not an option. small planets are good for both starship factories and research. and remember that focusing a planet means you can use one type of improvement to augment the production of another. that means that a certain amount of generalization can be quite helpful. that is why i tend to build 2 labs worth on almost every planet. so my eco planet of size 10 will usually end up looking something like 2 factory,starbase, 2lab, farm, 3 markets and colony. with only one farm i rarely need to bother with the morale improvements, but that changes in a hurry if i build more. 1 farm-0 morale. 2farm-2morale.3 farm-4 morale. you can build a monster economy with just 1 farm per planet tho.
if you do build research or production planets dont sweat the income on them but do put a bit of research on production planets and vise versa unless the planets are very small. a size 8 production planet should have no farms(unless you need the population to resist invasion), no markets(unless you built a farm
), 1-2 labs and the rest factory or manu capital. just that little bit of diversification can add a lot of flexibility to your empire, and flexibility is your main advantage over the ai. ai has efficiency, you have adaptability. you don't put the market on these planets because they will not help when you focus.
i only make one research planet unless i just happen to get a crazy bonus tile planet after i already built my research capital, but the 2 labs per planet is enough to keep me in the research game. that said i would still recommend filling those 6 and under with labs. it is just about the only way to make good use of them.
never forget that it is the money that counts. with a fat bank acct you can rush build a factory if you need to get your shipbuilding rolling, or just rush build the ship. you can take any of your eco giant planet and turn it into the most gawdaweful shipyard in just 5-6 turns if you have enough cash socked away
and if 95% of your planets are eco planes you will barely feel the pinch. this methodology is doing well by be at masochistic setting.
