First some basic warnings.
1. If you're on any anti depressants like SSRI's or SNRI's this is a bad idea, please reconsider.
2. As you're probably already aware, tramadol lowers your seizure threshold. If you take enough of it long enough a seizure can become pretty likely.
I forget the exact limit, tramadol isn't a drug I've done that often.
How much will get you high depends on your tolerance and your genetics and metabolism.
If you're a bad metabolizer it might not work at all. If you've ever used codeine, it's the same deal, so if codeine has ever worked for you tramadol should also.
Assuming you can metabolize it and most people can, it then depends on your tolerance.
A normal opioid naive person would be feeling decently good from probably as little as 50mg.
People who aren't opioid naive it's gonna vary, I'd start small, maybe 100mg, to get an idea how you feel.
Avoid exceeding 400mg a day, I don't think there's an absolute cut off, it's kinda like a dice roll, the more you're taking the more likely you might have a seizure. Ranging from negligible risk up to very likely.
This isn't an opioid you wanna be on all the time, especially at higher doses. Don't get me wrong when it's good it can be surprisingly good by opioid standards, but it has dangers other opioids don't.