Well 2nd thoughts are a healthy attitude to have...trees that big are more dangerous on the ground cause if you don't think it threw they'll roll on you when start limbing 'em.
That being said if it's a clear drop in any direction I'd give it some more thought. Just don't attempt it with anything less than a 20" bar minimum.
I think if I was going to do this I would want a bit more than a 20" bar to get half way through a 50" tree.
J.W Younger, as it has been said before, if you dont feel comfortable doing it then don't. Some mistakes you don't get second chances on.
Something to think about if you hire it done and want to do the cleanup is to let the feller know what you are doing and to leave some holding wood in the hinge so it is less likely to roll as you are taking off support limbs. I like blowdowns for this reason. All I have to worry about is the log settling and springpoles.
Go slow and take your time with each cut till the last branch is cut away. Think it through before you make each cut and be alert to what it is doing at all times. Never go at it alone. Trees fight back without a conscience.
It sounds massive. It should be quite an experience to be there when it comes down and the cleanup.
Hope it goes well.