Did you decide to follow Starting Strength? (Just curious)
You're not eating enough. Gained weight is gained weight, but "about 2kg" in two months is slow for a dude your size.
What, exactly, did you eat yesterday?
For heavy sets of 5, you could certainly push the rest longer. You shouldn't feel rushed or like being out of breath is a factor. You don't need to watch the clock necessarily, though glancing at it wouldn't hurt, but you should feel 100% ready to go. No burning in the muscles, breath all caught back, and mentally re-focused and ready to attack the bar again.
Eventually, yes. Right now, probably not.
Yep, it's definitely a long-running gym joke. The light bulbs, the ostriches, the Tasmanian Devils, whatever we want to call them. Really nothing you can do and it's not worth any mental energy dealing with them.