I'd probably try to put the microwave and toaster oven on separate circuits so you won't overload things. But, the tripping of the GFCI is a bit more troubling, as that doesn't trip on excess current, but on unbalanced power (i.e., some of it leaking and not following the return path). That COULD be an appliance issue, but it could also be a wiring problem where maybe there's a nail, staple, kink where the wire is caught between something and not enough to trip the breaker, but will trip the GFCI. It only takes an unbalance of about 5ma, where the breaker needs more than 20A, that's 2,000x more power to trip.
FWIW, I had a troubling circuit that would trip the GFCI intermittently with NOTHING plugged into the circuit. I eventually tracked it down to one segment of the daisy chain, and replaced that wire...it's been fine for years since. Never did figure out what caused it, just ran a new wire...probably a nail or something, and depending on the humidity levels, or the whims of the gods, caused it to trip. It could also be a defective GFCI, but that's much rarer (I'd tried replacing that first to no avail). At the beginning, this might have only happened once every couple of months, but over several years, it started to occur more often until eventually, it would not stay on (i.e., wouldn't let me reset the GFCI) at all, which is when I finally got around to fixing it. It was easier to run a totally new wire from the panel than stringing a new one between the two receptacles and I abandoned the defective one in place.
This is a case where a megger might verify whether the wiring was suspect. Those are similar to a DMM on ohms, but they apply a high voltage on the wire and look for leakage to verify the insulation is intact. They aren't inexpensive, and an electrician may not own one, but it is a good diagnostic tool for checking wiring for faults...if it were a direct short, it would always trip the breaker, and that's not the case here, so it takes a bit more specialized tool and the knowledge of how to use it.