I'm finally getting my garage walls and trusses soon. If I'm pretty sure that I will use a mini-split in the future should I leave an access hole for it before thesiding goes on?
I wouldn't worry about an access hole. (I assume you mean for the line sets.) If/when you install the mini-split you'll cut a hole through the wall. The inside unit is mounted over the hole, a line set cover goes over the outside.
I would have your electrician put in a disconnect where the outside unit would be installed.