... the velcro acts fine when sliding in and out. There is a bit of a step between the two layers, but you can just space the pedals to compensate for it, or double up the velcro on one side of a pedal if you need to go over the join.
I also prefer the single rail boards I think, and the XPND works really well in that department. The bag is expensive for what it is, so you could consider getting a Pedaltrain Nano Max, keeping the bag and selling the board to get a decent bag for less ha ha!!
For a PSU the Cioks DC 7 I think just squeezes under there (check you tube for what it looks like). I'm currently using a daisy chain with mini pedals and for a quick pedal change around if needed it's great.