Firstly, welcome.

A good CNC machine should be able to hold an accuracy much better than 0.1mm but you'l need to work on the ballscrew nuts to get down to low levels of backlash to get the repeatability you need, but its certainly feasible The trick with double sided anything is the jig you need to ensure the part is exactly in the right place when flipped. The simple solution is a hard edge to push the board against, the difficulty is getting repeatability as the slightest dirt or swarf will give an offset. The best solution is a 2-part frame into which the board is placed which has locating pins that guarantee the registration from either side. This could be made from engineering plastics (delrin, HDPE) on the machine itself.

I cant comment on the MD A4 kit as I've never seen one, however I have heard some 'less than complimentary' views. I'd have a think about the Kress spindle, it will certainly do, but runout can be an issue. I beleive there are some simple bearing upgrades to improve it. The 3Nm motors are a bit overkill for an A4 ballscrew machine but will serve for a bigger machine later.