Couple things here.

1. I did my own stainless liner install for my wood fireplace insert. My approach was to give it a try and get help if I couldn't get it to work. It worked fine.
2. You should look up the installation manual for your furnace and water heater; many of the new high-efficiency ones won't work properly with a 5" vertical exhaust. You may be able to vent out the side of the house instead.