Use 175 energy to grow a brain large enough to have some sort of conscious thought, even if it is just a fusion of pants-on-head retarded and inbred-monkey stupid.

Use 100 energy to evolve into a more deadly disease.

You people are so bad at this. LOL LICK STUFF XD
List current abilities and characteristic of our disease, sir Clam.

You have the ability to divide, absorb cells for energy, your 3 cells in total add up to a total power storage of 600 units, you also have rudimentary sight and feeling.
It will require 400 energy units to evolve a very rudimentary brain and will require at least 30 more cells to convert into a simple synapse network.
Specifics will be required to "Become a deadlier disease".

spend half of our power to divide all cells, and begin genetic permutation to produce more efficient mitochondria to improve energy production.
OR
adapt to be able to metabolise the most abundant substance present in our environment bar water, and divide 2/3 of our cells meiotically to get some genetic variation out there.

Your three cells are now 6 cells.
You have 100 units of power remaining.

Seek some more organisms to assimilate and gain energy.
If possible with energy supply, evolve ability to encapsulate to survive rapid environmental changes.

You assimilate 3 smaller organisms and come across a much larger one, all 6 cells will be required to absorb this one and it could put you at a risk, attack?

Kill it, eat it, and see if you can adapt any of its traits for your use.

You carefully flank using all six of your cells, two are lost to it's poison.
You've got a full store of 800 units of energy, 200 per cell, you've also absorbed the enemy cell's poisonous nature, if you wish, for a toll of energy, you can become immune to poison, after that, you can use more energy to become poisonous, and after that, you may evolve an offensive poison jet trait for a toll of energy.

How much energy for each, and I assume it will effect all 4 cells?

200 for the first upgrade, 400 for the next, 800 for the last, affects all cells and all cells divided later.

Does this decision have to be now or at any time?

At any time.

Radsauce. 200 for poison, and give prospective energy cost of replacing those two cells we lost and tacking two more on.