If I use a Shadow Key to the gate of a Shadow Lair, is it open permanently to me?
What I mean is, for example, I open a Lair and go down it but I don't complete it. Is the gate still open?
I know I sound foolish asking this, but I want to be absolutely sure.
Shadow Key use


................Ouch.
What if I DO complete it?

Every attempt at a shadow lair requires the gate to unlocked with a new key. Generally, party members will split the cost of the key with the leader before the gate is unlocked, bringing the price down to a more reasonable ~450 ce per person.

How good are you? If the answer is anything less then BAMF, then probably a poor choice unless you want to dump even more cash into revs.
People do solo SL, but these people have usually already ran them many times in parties.
Find a group & share the cost of the shadow key (450 CE each you you buy one for full price).
Also you are going to want to save up at least 800 CE + 5,000 cr more so you can craft at least one armor piece while you are there. Check the wiki to see what other materials you need and make sure you are doing the SL run that will give you the unique material that you need for the craft (unless you already have all the mats, then it doesn't matter which one you run). Even better save up enough CE, cr, and materials to craft a whole set while you are there (unique sl materials can be purchased at the AH).

Since you haven't done them before, no it isn't reasonable to go solo unless you can solo regular FSC blindfolded (literally). Find people you play with normally who want to go in on the key price with you (or if you have money to burn you can always invite them for free).
Go with at least 2, since it keeps energy rev prices down and you can revive each other with health. A party of 4 cuts key costs the most.
I did the ice queen as my first shadow lair and we probably used 6 energy revives (so 80 energy spent total). If you read the wiki, you can make sure you are bringing the proper gear for the monsters that will be in the lair.
Nope. One key, one attempt.