Ok, not trying to be an a$$ or anything, but you say you JUST went for your first real ride yet already know if leather will be too hot or not? Eh, never mind. I won't do my whole preaching thing, everyone ride their own ride.
Just make sure your jacket fits well, that's really the most important thing.......though with mesh I'm not even sure about that. Take a fall and it won't really matter if it had fit properly. A riding buddy of mine has the FirstGear one you mentioned and it *seems* to be of reasonably good quality FWIW. I don't have any personal experience with Teknic gear.
If you're looking for lightweight breathable protection, you could look in to the under-style armor that you wear under your regular clothes if that would be a viable option. Several of the major gear-makers have this (Alpinestars, Thor, Teknic, etc) and I think the most well known one would be the Bohn under-armor (there are pants and shirts). Honestly this would probably give you the same amount of protection as a mesh jacket will, they are essentially the same thing; one is meant for under and one is meant for over.
Eh, hope this was somewhat useful
Ride safe