For the big boys out there who have been playing for months:

What is a good trade-off between planet size and resource availability? For example, an Average Size Rich Resource versus a Massive Size Average Resource?

production level upgrades are easily available... go for the largest possible planets and ignore production level

How do you upgrade the production level? Doesn't it cap after 5 days?

He's referring to the Availability Bonus (Rich, Very Abundant, etc) that is easily boosted with several different artifacts such as Toxic Purifiers, Terraforming Devices, Planet Data Optimizers, etc.

if u r new, just do a hypotherical calculation based on ur current techs AND the 7 different AP pull structures to see which one would yield more.

But if you are look at long run(passing rank 250 and can farm NPCs for production boosts and get race changes, for example)
1. the bigger the better, regardless of aviliablity
2. AP is better than RP/MP
3. Icy and terra etc are the best for each size, because they can be expanded(meh... i think there are a few more but off the top of my head~)
I would suggest you look up the wiki artifact section to find out which planets can be bumped up via the various means, those would be better than most. (although in case of metal to dyson, as it hardly matter what kind of a metal you start of with.... u don't need to pay any special attention)

P.S. other than the bunch of artifacts that can upgrade aviliability, there are also the 3 races that can boost 1 type of each. The first one is the +research one which is unlocked once u complete the chain starting with Anomalous Appearance(a mission), it's gonna take quite a bit of effort, but it really helps once u r done.

OK, sorry for being such a noob. I guess I should at least go read the wiki

oh good heavens no... just post in the legion forum saying you're looking for a beginner's legion... a good beginner's legion can teach you what you need to know

use the wiki as a reference tool

For toxic and gas planets go for the largest size, for others you have to compare all the resources and the size. I do not put any defense or cloak on anything large or smaller. A mediocre planet without defense can produce as much as a well defended good planet.