Hi Beano, that's a good looking maple.
I received a similar one also about a year ago from Neil.
You and I seem to be at a similar stage in our bonsai travels so this may or may not be of help.
My first move was to get it into a bonsai pot immediately !! but resisted the urge somehow
Instead it went into a wide plastic tray type training pot to grow more taper into the lower trunk.
After seeing the growth it put on I'm stoked I went that way because taper has improved a little already
This season I'll do what I should have done last year and place it on a shady garden bed so roots can escape the tray.
IMHO all good maples have trunk taper and developed nebari. However that means going the slow road, loads of time.
Then again I do have a thing for nice wide tapering butts

If your happy with the trunk then just power on.
cheers