So you're in Iceland? Cool! Miniar's not the only one now (at least, I think he was the only one before, but I don't know everybody here).
None of my ex-cats responded differently when I started T. My new boy, of course, doesn't know any different.
I do injections and prefer them over creams and gels. Time and time again, I have heard that injections produce faster results, too. But I imagine that after a certain point, it would no longer matter. If you have mood issues, you might stay more stable on a gel or cream. I don't know anything about implants. You might talk to Miniar to find out what's available in Iceland.
I was pretty overweight when I came out for the final time (I went through a protracted sequence of different coming-outs, then went back into the closet). As soon as I did come out, I started a weight-loss campaign. I lost quite a bit of weight pretty quickly, but I have found that it is definitely easier to lose weight and maintain weight on testosterone.
There is some contention about some baldness issues--whether XX people are more or less likely to bald. I've seen the genetics laid out in some detail, but my biology is a bit rusty. But some of us do lose hair, and we tend to get a male hairline. My hairline looks just like my brother's and father's. My hair thinned--I still lose a noticeable number of hairs every other day, but the density seems to be constant--and the hairs themselves are coarser. I'm not sure whether the coarseness comes from aging, T, or both, but it suits me; my hair used to be like spidersilk, and it was murder to have a loose hair on the inside of my shirt, where it could tickle me mercilessly. The things were so fine that they were practically impossible to track down and remove.