- make the footprint pads as big as possible,
- make holes in pads for drill easily
- you can work minimum 0.3~0.4 mm trace width.
but i suggest work 1mm in general.
it is hard to build double side PCB, but it is possible.
but i think double side custom PCB is nothing without plated holes.
plated holes are very important for a double sided PCB
actually, it's not that hard doing a double layer diy pcb.
It is a matter of well aligning the sides, and making the holes big enough to properly drill them..