1. Can anyone give me a few tips on colonising planets? Like is it worth it to colonise a Very Massive but Sparse Gas or an Average but Rich Barren?

2. Is it really necessary to guard and defend planets? Because some of the enemy planets I see don't have any attack or defense on them...

Hope someone can answer my questions.

neither one of those would be good to colonize

depending on the planet it can be. the ones you listed no. because they are worthless and people would want them stolen.

Generally you want to be going for large+ and rich+, obviously if you have a small planet but with say mega rich resources that's fine too, so you can trade off space for more production on that rule. You don't want to be putting defense on your planets at all just yet. Get as much production as you can out of it then when you eventually unlock Obviation Shields, then you can start thinking about defending your planets properly.

Oh, ok. What I actually mean is the mininum stats I should be going for when I want to colonise a planet. Has someone made a topic about it?

PS And how important are cloaking and planetary population?

Follow the advice above Large and Rich minimum. If you look at the wiki, it will have the various sizes and richness of planets. Start with Large/Rich as your base and work from there (i.e. Avg/Very Rich or Very Large/Ext Abun would be fine) Converting to strictly numbers to better illustrate, Large = 0 and Rich = 0, every size or richness factor higher gets +1, lower gets -1. Make sure you maintain at least a 0 avg. Obviously the higher the number the better. (Small/3xMR = -2/+7 = +5 would give more production than a Large/Rich). Hope this helps

I'll add about the def/att

General rule is NOT to defend them - with cloak, att, def, pop - unless it is a very good planet.

For cloak - don't bother to cloak them - unless you got the best planet cloak (inverse flux jammer 800 cloak) and got some % cloak artis. If it is an EXTREMELY GOOD planet - which ppl usually after, you may want to super-cloak it.

For att/def/pop, it only deters low levels from taking it - but not those in a legion, which usually got some high rankers in it - so don't bother to defend them.

You should ONLY think about serious defending when you got 600/750/1200 def structures, other than that don't bother placing def structures.

But I thought attack and defence should be very important for my rich planets? Just in case someone takes them? And what about cloack to prevent others from scanning it and population (As I know it, population is hull for a planet) so my planets will need more energy to be invaded? Someone explain them...

if your planet is mega rich+, then don't bother defending them - with def/att/cloak, because higher rank always managed to get through them
for average planet - large/rich - try to get def at least 2k (with legion bonus) at rank <150, 4k at <300

if you're defending a planet (against low rank - that is <400) pop usually doing pretty good, but against high rank they can drop quantum bio vaps and easily take away your planet. Just make sure you don't get 0 def

What he's saying is your low researched defenses won't stand a chance against the bigger players, so you'd be better just maximizing production anyway.

Whenever you take planets, you have to think about balancing its defense (and in this case, defense includes any structure that can slow down an invasion) and its production. Sure, a mega-colossal, 40x mega rich planet wth 40 mass shields (for what, 18000 defense pre-legion bonus) on it may seem well-defended, but it will do you no good if you can only get 20 points per hour off of it. In addition, most high ranks would be able to take that defense without a problem, anyway

Therefore, the best thing to do with planet defense is to use the structures that give the most defense for the least amount of space. That's why structures before the planetary shields aren't really worth it - you use a lot more space for defense, sacrificing valuable production (if it's minerals, you're losing out on credits to buy better structures; if it's research, you're losing out in points to research better structures; if it's artifacts, you're losing out on chances to grab android scientists or other artifacts that you can sell or improve your ship with)

...I had more to say, but it's too early on a weekend for my brain to be fully functional so I forgot. xD I'll probably be back later to add to it