i'm no expert but here's my opinion: the way a motorcycle transmission works is different from a car's. motorcycles are "constant mesh", meaning that all gears are spinning at the same time. instead of the gears sliding to engage, a set of "dogs" on a plate slide into holes on the gear to engage that gear to the output shaft.
image taken from
http://www.vf750fd.com/blurbs/shifting.htmlso basically, the gears don't grind, the dogs do. your dogs could be worn out, in which case you should give them some water and a treat and a nap
or your holes could be elongated/beveled, and if that's the case, you should see a doctor
honestly, this is probably worst case scenario, but unlikely. worth considering though and would explain the grinding sound. also if you clutch doesn't completely disengage, it would explain the grinding between 1 & 2. it will try to go into neutral between them. if the idle/engine speed is too high, it would be hard to shift out of neutral from a stop (high engine speed can't match low road speed), as the little dogs would skip over the holes too fast to engage.
lots to consider. GOOD LUCK!