Answers

If you want an efficient fireplace, I recommend a full insert (sealed-combustion) that runs a new vent pipe, typically up your existing chimney. Hire a professional installer from a local fireplace company to do this. 

There are also options to retrofit a "gas log" in an existing fireplace, but there are several issues with this. Typically, if you have an open hearth without doors that seal tightly closed (with a gasket) then you are going to put more energy up the chimney than actually radiates out into the room.

Both, more than likely. The mason should replace the masonry products and the roofer should work with the mason to achieve a regletted counterflashing and flash the roof under counterflashings.

Each case is unique but in general, the chimney should be done first. Special attention should be paid to the roof flashings around the chimney.  If the flashings are behind the stone then make sure they extend far enough into the shingles so the new roof can be flashed properly. If the flashings are surface mounted and there is a counter flashing then the roofer should have no problem making the chimney base watertight   

http://www.ncsg.org/  The National Chimney Sweep Quild is a great source for licenced and certified professionals in your area. If they don't do the work, they will know someone in your area who does.

Philip Anderson

HDR Remodeling

Berkeley Ca

No, but have you thought about contacting a manufacturer and asking for a local referral. Sometimes it is an unknown fact but home remodeling product manufacturers have authorized dealers and installation crews listed on their site! This guarantees the best match. We always explain to homeowners having a certified installer is more important than price! Residential Renovations works very hard to make sure all installers from roofing, siding and windows to decking, sunrooms and beyond is installed by professional crew members who are trained as the manufacturer warranties. Good luck with your project! You can visit our website at www.ResidentialRenovations.com to learn more about Residential Renovations - serving Ohio and Michigan homeowners!

There are a very wide veriety of gas fireplace inserts.  

1. Check with the city to see what you can install.  Some cities are now requiring sealed units

2. Do not try runing a gas line by yourself.  Hire a licensed plumber to do it.

3. http://www.csia.org/?gclid=CL_Qk-SZ0dACFZBefgodOrUNRA Contact a CSIA certified chimney sweep to help you install. 

Thanks

Philip Anderson

HDR Remodeling Berkeley Ca

Brick mason

Masonry work first. Best, Ken