#1. If your door is going to travel more than 8 feet due to the lengthened tracks, then your guy is correct. If the door is NOT going to travel more than 8 feet with the extended tracks, I think you can still make it work. The limiting factor on this door opener is the total lift (8 ft), not the track height.
#2. I called Lowes when I was first looking for this drive. All the lowes stores in my area did not have them on the shelf, but I could order one. The price was about $100 more than where I purchased mine. Never had anyone say there were problems with these units.
The i-Drives are warranteed for 5 years for Parts & Labor and have a lifetime warrantee on the motor. That's a better warrantee than most door openers out there.
Not that I'm plugging these openers. I just did a couple of months of research before buying these.