I believe you can find basic side effect info in Hudson's FTM Resource Guide and possibly Nick Gorton's online book about medical transition for FTMs. But I wouldn't count on finding any specific studies. Even the doctors who "treat" us sometimes spout misinformation. For example, I keep being subjected to the "higher risk of cancer" spiel at the clinic where I go. When I challenge the doctor to show me one substantive study to back up such claims, I get crickets. The most I've seen is a paragraph in a medical text stating that there IS no evidence that T causes a higher risk of cancer in trans men. This doesn't mean that there isn't a higher risk; it just means that the problem hasn't been sufficiently studied. If there is a study out there that goes either way, I would love to see it.
Part of the problem is that many of us are eager to get rid of the offending body parts as soon as possible, so long-term monitoring isn't always valuable. We already have a relatively small population base for studies, and the researchers would likely want to have a good-sized sample of trans men who are just about to start T and who, by the end of the (probably lengthy) study, still haven't had surgery on the body part in question.
And then there are the possible side effects on other systems/organs...