Hi, Kristen,
I'm really sorry to hear that you'll only have a week in Scotland! However, I'm sure that you'll make the most of it!
First of all, if you enjoy traditional music, by all means avoid the the tourist shows!!! They are definitely not authentic, and no self-respecting Scot would be caught dead attending one of these events, unless he or she had been dragged along by a relative who threatened to disinherit the person if they didn't attend.
There are traditional music sessions going on most days/nights at Sandy Bell's, on Forrest Road, just a short walk from the National Museum of Scotland. There would most likely be a session on the afternoon of the 14th., if you're not exhausted after your flight. You can get more information about Sandy Bell's at www.sandybells.co.uk or you could ring them once you arrive in Edinburgh at 0131 225-2751, to find out what's going on. Another pub for sessions is the Royal Oak, but I'm not sure what days they have music.
The Leith Folk Club has a concert on the 16th., but unfortunately, it's a bluegrass duo! The Edinburgh Folk Club has Kieran Halpin coming in on the 17th. He's an Irish singer/songwriter. An excellent songwriter, but definitely not traditional.
Unless you really have your heart set on it, I would skip the day trip to Loch Ness. As you basically have only six days, a trip to Loch Ness would take up almost a whole day, leaving you only five days for everything else you've planned. As you've probably learned from visiting this forum, Loch Ness, although large, is not the most attractive of Scotland's lochs. It's big, and it's wide, and it has a large plesiosaur hiding somewhere in its depths, but your time would be better served by visiting a loch closer to Edinburgh.
There are many churches of all denominations in Edinburgh. You are bound to find one for a Good Friday service. I'm sure that St. Giles Cathedral (Church of Scotland), on the Royal Mile, will have Good Friday services, or perhaps one of the churches (Church of Scotland/Scottish Episcopal/non-denominational) at Holy Corner. There are two things that you should know: Scotland is one of the least religious countries in Europe; and Evensong is more associated with the Scottish Episcopal Church than it is with The Church of Scotland. You may want to try St. Mary's Episcopal Church on Palmerston Place for Evensong. Glasgow Cathedral sometimes has Evensong, but it's mainly for television broadcast. The Cathedral and Necropolis are definitely worth a visit during your time in Glasgow, even if there is no Evensong scheduled.
Visits to Stirling, Glasgow, and Falkirk can easily be done by train; Rosslyn Chapel can be easily reached by bus or taxi. If you have the time, a walk up to the top of the Scott Monument would be worth it, and with any luck, there may be something musical going on in Princes Street Gardens.
One of the best places in Edinburgh for an upscale afternoon tea is in the top floor tearoom in Jenners Department Store on Princes Street. Try to get a table near the window, even if you have to wait for a bit. The views out across the Princes Street Gardens and the Scott Monument are worth the wait.
Have a wonderful time!
Slainte!
Mike (Auchterless)