1. Don't know what that old "orange bird" pipe is made of, but it was probably installed because it was cheaper than cast iron back then. Any sectional pipe is subject to root intrusion, and the best solution to sectional pipe root intrusion is to replace it all with glued plastic pipe (white PVC or black ABS), which won't allow roots in.
2. A Fernco neoprene rubber sleeve boot should be o.k., but a no-hub (aka mission) coupling would be better.
3. As long as there's no compaction of the ground over the pipe (driving over it, etc.), it should be o.k. in gravel, but sand might be better...nothing to crack the pipe against.
Just my opinion.