Hi, I have only just started testosterone but I have been using men's bathrooms for almost a year now and have never had any problems. It is legal in most places, but you'd have to look at your own state/country's legislation to know for sure.
If I wasn't at a stage where I would pass most of the time then I'd only use the men's bathroom if I were 100% sure it were safe, but that is just my preferences. I am very lucky in that even before T I never had any issues passing (although I did look a bit younger).
As for tips, if you aren't sure if it is safe, disabled toilets are your friend and you are perfectly in your rights to use them. If you want to use the gents but are a bit unsure then walk straight in, straight to the stool, do your business, and get straight out (bring hand sanitizer and use that after). Also, so many guys get worked up about using the stalls, toilet paper, making the wrong sound from urinating from the wrong height, and are worried about bathrooms even if they pass 100%. In reality, heaps of cis guys are "pee shy" and use the stalls, and even use a bit of toilet paper to clean things up at the end. Also, guys use the toilets for going to the toilet and are only bothered with that, you are less likely to be clocked in the toilet because people see what they want to see, and, finally, nobody is listening to you pee.