Beautiful looking mill.
If you plan to move it occasionally then that rolling base looks like it is very capable but - as a “tip” - I’d prefer to find a spot and level the stand feet on the concrete floor. Bolting the stand to the floor or not bolting down has been debated. Some people would suggest putting it onto hockey pucks and others use vibration isolating feet. I (right or wrong?) put mine on 1/4” rubber pads and the snugged it down (bolted) to the concrete.
First “tip” - undo the 4 bolts holding the mill base to the stand. Those bolts can put an uneven pressure on the base and cause it to warp. Use a feeler gauge at each corner to determine which corner has a gap. You can also use a small pinch bar to apply the same upward pressure at each corner and help find the corner that needs a shim. (It is extremely unlikely that all corners are on the same plane.) Then tighten the 4 bolts gradually - 5 ft lb, then 10, then 25 and finally 35!ft lb.
There is a ton of other things to do - but getting it level is a good start.
PS 1: levelling (as described above) is more important for a larger mill and maybe overkill for a mid sized bench top mill like yours. My bench top mill is just a little bigger than yours & I put a lot of effort into levelling it.
PS 2: You can leave it on the rolling stand and still level all corners on the concrete. Then later moving it would be simple.
I built a HD rolling stand for my small lathe. When i finally figure out where it will be located, then l’ll level the rolling stand.