SE5 is easylith with two additives.
C additive is basically sodium sulfite
D additive is Potassium Bromide and another restrainer.
If you are just starting out, you'd want to play with easylith (A and B) for awhile.
Trying different ratios and different papers within those different ratios. And there is the use of 'old brown' or not....
That right there can consume lots of time (I know!) to give you a better idea about what is going on and what kind of 'look' you are after.
You might find what you want and not need to adjust the mix any more.
If you look at the instruction sheet there are some key points at the end of the second page
It tells you what more of each solution will do to the resulting print (as a guidance).
Also, the easylith instruction sheet has a troubleshooting page that tells you what it could be and how to fix it. Lots of times, adding D (bromide) can resolve or minimize the problem.
With those two instruction sheets you should have plenty to play with.
Believe me I know!