Let’s split it into 5 sub-stages: Planktonic (20-1,000,000 cells), Nektonic (1m to 100b cells), Aquatic (100b+ cells, does not matter how many cells you have), Amphibious, and Terrestrial. Also, every evolution should be 10 my apart.
Planktonic: At first, growth is slow, but later, it starts speeding up as you can build cell groups, which are the building blocks for the later plankton evolutions. What the cell groups are made of is self-explanatory. These groups are unlocked after you have at least 100 cells AND 5 cell types for at least 5 generations. These can be made up of a max of 20 cells. When they are unlocked, you also unlock sexual reproduction. This allows you to not start from 1 cell every time you reproduce, but at the cost of finding a mate. After you have 100 cell groups and 5 different cell group types, you unlock tissues. Tissues are made of a maximum of 40 cell groups. The ultimate group in the planktonic hierarchy is the supertissue. These are unlocked when you have 300 tissues for at least 5 generations. They are made of a maximum of 50 tissues.
Nektonic: At this stage, your size is measured in cm. You go into this stage after you have 500 supertissues. This is when Organs are unlocked. These are made of a max of 6000 supertissues. You exit this stage when you are at least 70 cm long and 20 cm wide, the size of Acanthostega, the first tetrapod. You can also evolve bones and/or external armor. You must be in the mesopelagic or sea-surface environments to evolve into this stage.
Aquatic: You can evolve to be much larger. This sub-stage can be quite short, as you exit when you are 1.5 meters long, around the size of Icthyostega, another early tetrapod. However, you can become very large, maxing out at 25 meters long. You can become intelligent, or go onto land.
Amphibious: You go onto land. This is where you can go onto land, but can’t exit the water. You are still tied to the seas by you reproduction. This is essentially just a warm-up for the next stage. You need strong enough structure to go onto land without collapsing. This is where bone comes in. Without bone, you can’t walk on land. You also need respiration that will work on land. Lungs are what is needed for this stage.
Terrestrial: You can now exit the water fully. This is the final step before awareness, assuming you went through the amphibious way and not going the sea intelligence route… You can become a predator, go into the trees, or go back into the water! After evolving your brain enough, you move on to the Awareness stage.