as long as your are using a co2tank pressure is nothing to worry about.
what you need to be concerned about is keeping the beer line cold once it leave the freezer in the garage.
you can DIY this, but your best option is going to be a Gylcol system made for long runs of beer. You ca try and fashion your own Glycol system for cheaper or just splurge and buy a tried and true setup.
air is not going to do it for you, you need to run a cold recirculating glycol along your beer to keep it cold.
its doable, but not cheap.