It would be extremely difficult for us to give you a useful answer on this one. Specifically, the Kratom is what makes it all so dubious. It's dried plant matter, not to mention it's essentially unregulated in any way. Just like Poppies or Cannabis, the actual potency is going to be determined by the proportion of active substances, in this case Mitragynine(s) relative to the rest of the bulk. As Kratom is uncontrolled, the potency is going to vary pretty widely.
Even if we did know the potency of the capsules you have, as in how much Mitragynine(s) they contain, we do not have a very good understanding of Mitragynine to begin with. It's been used in traditional medicine in its home regions for a long time, yes, but Western Medicine has yet to study it to the extent that we would like.
What you get in the end is that you are actually the authority on this. The way you react to the different drugs/dosages, how does the Kratom moderate your withdrawal/dependence? The easiest way to find the closest approximation you'll be able to get, would be to see how much Kratom is required for you to be well, but not sedated. This will at least give you a ballpark estimate. However, this can all change with a new batch, new cultivar etc.
If you had to pick one or the other, I would avoid Tramadol. It's a drug that seems to cause a lot of problems. Considering there are plenty of other options out there for Opioids of similar strength and effects, it seems unnecessary for Tramadol to even be prescribed. As you've said in this thread, seizure risk goes up immensely when dosage of 300mg Tramadol or more is taken in a sitting. Again, considering Opioids are so prone to tolerance, dependence and abuse, it seems like asking for trouble when the seizure threshold is crossed with such a low dosage. Addicts often make bad decisions, and I can totally see an addict contuing to take Tramadol, have seizures and still not be able to stop taking it. We see worse things in Harm Reduction.
So if I were you, I would stick to the Kratom and forget the Tramadol. This is especially so considering you yourself have had a seizure already. Figure out what dosage of Kratom you need, try to find a legitimate supplier and establish a stable means of acquiring it. Once you find a variety that works for you, you can order in larger quantities to both save money and give you more security.