8- 4- 1- 1- 1- 1 Is probably fair even though it would cause more tiles from terraforming. Remember each extra planet would cause more production from population. If your starting homeworld is aquatic then you probably should get advanced water world colonization as a,starting tech. If you made them extreme  planets then you could make the other five 8- 2- 2- 2- 2. If you do start with advanced aquatic then they should be some other extreme planet.

I noticed I didn't clarify something on my second idea your homeworld should be an eight wether terran, or if you have advanced aquatic colonization only then have you home world an aquatic world. This is based on your 8-4-1-1-1-1 Now if you make the other extremes then they could be double class because they have double production. This would also be sweeter if you are aquatic. Now if the other are extremes due to half production then you Then you can double the class making the system 8-8-2-2-2-2. With relatively the same effect. Your idea of combining adaptive with aquatic maube you should try this. If you apply this rule to every one including your home without advanced aquatic world colonization then you could double all of them due to half production then it would be class 16-8-2-2-2-2 this probably is acceptable because aquatic uses a trait that could be used somewhere else. But if you think this is to powerful with aquatic then you could scale is back to 12-6-2-2-2-2; then try this. Unless your homeworld is either terran, or has advanced aquatic world colonization it would be 8-6-2-2-2-2.

Crusade will change a lot about my arguments. Also my experience is based on medium to huge map sizes (~6-12 planets without conquest per civ).

But for the current game, I would argue the following:

What do you pay for colonizing a class 1 and what do you get?

You pay the manufacturing needed to build a colonizer (cargo hull with colonizer module and nothing else) and the time lost for population not producing anything during the travel.

What do you get:

Colonization capital
 - 5 food
 - 0.2 growth
 - 1 production
 - 3 adjacency for Manufacturing/Research/Population and Wealth.

In short: it is amazing for its cost.

What happens next? Well you use the production you have to pump out economic starbases. By hitting 6 worlds at the same time, they are extremely low cost improvements again (2 constructors in return for +5% production and a basic factory on all worlds essentially).

So what about the drawbacks of class 1 worlds? Since you have many, just screw building hospitals, you will be far ahead in population growth anyways. Screw building planetary factories or research stations, since you can put those on starbases. The only thing you will build once you can terraform, are food improvements, which will scale nicely with all the starbases you have. Screw building scouts, developing these six worlds might be all you need.

Btw, which techtree will you use? If you are contemplating something like thalan or drengin: Thalans benefit form hives a lot and have the hyperion matrix, which affects all planets. The drengin have their slave hubs, which are easily one of the best colony uniques in the game. You will get 6 of these very early!

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Long story short:

I think 8-4-1-1-1-1 would be overpowered even before considering terraforming. But by the end of the day, you are playing with it, don't push the balance so hard, you will lose motivation

I hope this was somewhat inspirational to you.