Not shure for bit burning but I would suggest to use a ""fool proff"" shaking grates system. On the 3 models of stoves I had, the one in the G.B. seems to be the best. Having the outside round rotating grate makes the coal bed moving just what it needs to clear the outside ash down , then the centered triangular grates send ash down. NEVER bridges, never at all.Takes just second to clear ash as much as you want/need to. In the sunnyside, there is just the round grate for the entire grate surface and once in a while poking needs to be done to avoid bridging. Not a big problem but very far from the Vigll and the Sunny shaking chore.
Make the fire pot's wall/s completly vertical to avoid ash build up.
Make shure there is no horizontal part at the fire pot's bottom to pile the ash. I mean no moving horizontal part.
Make shure all the ash falling down go in the ash pan. Some deflectors can be easily placed under the outside of the grate so the ash falls at the right place.
Make a sort of sliding out ash pan and sliding lid like Vermont Castings stoves have.
Top and front loading doors.
Long gases path like in the base burner with damper to direct the flue in direct or long path mode.
Build in MPD.
And make a beautiful stove...so you can admire the stove 12 months of the year
Most of the items mentioned here can be found in many antique stoves.