From previous threads on here, Sketchup is not very good for creating useable STL files to slice and generate g-code for your printer.

Plenty of free design software available, personally I use Fusion 360, there are plenty of how to videos on YouTube for it.

As for using an ipad or simlar, someone with more tech knowledge could answer that.
It is doable on a laptop, but a lot easier on a larger desktop machine.