Building your perfect bench will only come from many years of experience and knowing whether you prefer face vices, should vices, leg vices, end vices. etc etc.
Something along the lines of this bench will provide a sturdy surface and with the addition of a bench hook and shooting board will be sufficient to build just about anything.
Make a Leg frame, simple mortice and tenon joints
Then make another
Screw some chipboard to the back and another piece to the base and attached kitchen cabinet legs to the underside and test for strength with anything that comes to hand.
Take an old office desk top and plonk it on top. This was very heavy, 1" thick and thick melamine type covering top and bottom and was very flat.
Add some beech lipping to 3 pieces 18mm MRMDF and glue together
Check for flatness by balancing steel rulers on the top.
Reverse mount the morticer and using bench dogs to insure spacing is equal drill lots of holes
Screw a couple of old kitchen cabinet doors to each end to add rigidity and weight and add a kick board to stop bits rolling under.
For planing long lengths attach a Gripmaster
If after all that the bench still wobbles or racks it could be screwed to the walls of the workshop and even the floor. no need to in this case.