How far away from your freezer is the tree?? I would consider running a large diameter pvc pipe (same diameter as your tree) from your freezer to and possibly into the tree allowing the freezer to keep this air cold. You could wrap the pvc if you want in some insulation, to minumize the thermal loss. If your Tree is a ways away I would do the PVC trick and then install quick disconnect devices on your beer line. Then pull the lines through the PVC after attaching a nice size line or string to help the lines back through after cleaning and visual inspection. Star san is a good lubricant too if things get tight.
Most Trees have insulation (foam) on the inside that prevent sweating. Commercial Kegorators are a good example, however this is helped by the refridgerating unit keeping this area cold. This is why I would use a Large PVC Pipe to connect the two.
I run maybe 6ft of line in my refridgerator from keg to tap and it works fine, I despense and carbonate at 10 psi normally, unless I'm using a carbonating stone. Your beer line length should be more than adequate.
Oh and by the way your bar build is quite impressive and spot on!