While in theory this seems like a nice thing to do, I tried to do this and it has one major flaw which in my opinion takes the fun away from it. To use GC planets in Advanced Rocketry you have to put the Dimension ids from GC into the planetDefs config from Rocketry. In this config theres an option to control the gravity on the planets you're making. When you set this gravity to something else than standard it causes gravity to act weird due to GC gravity and Rocketry gravity conflicting, on the moon for example you will get yeeted straight back to the sky. Now you might think, ok, I'm just going to set the gravity to standard in planetDefs. Well, here comes the problem: the gravity setting also defines the size of the planet in the planet selection screen, so when you set them to standard value all the planets have the same size, which just looks horrible. Tl:dr Tried it, gravity said no, don't waste your time doing this, try using biome mods to get more varied planets instead. More on reddit.com

ExtraPlanets is pretty much just a grind, not sure what kind of tips you are looking for. The most obnoxious part is probably getting the shield generator from Venus - the corrosive atmosphere destroys your space suits so fast you really gotta rely on other mods to figure out some way to survive. Once you get past that hurdle it’s really just the same loop: mine hundreds of each planet specific ore, make one million heavy duty plates, upgrade your space suit and thermals whenever possible. Repeat till you die of boredom or get to Kepler. One thing I will say is that the Extra Planets experience is made a lot less unpleasant when you have a ton of other mods to streamline things lol More on reddit.com

Ugh, this is one of the reasons I never seriously tried PO2:K. Galacticraft proper isn't that bad, as it only has a few tiers, but with addons, it's just uncreative. I was thinking about a pack which would include both GC and AR, but where you would need to progress to the asteroid belt using the GC system to get the resources needed to build a modular rocket and venture further. More on reddit.com

Galacticraft-planets is Galacticraft, if you look at the GC homepage you can see the mod is split into 3 parts https://micdoodle8.com/mods/galacticraft/downloads A core mod, the base mod and the planet mod. More on reddit.com