Larry, I don't mean to be a wet blanket, and I get tired of harping on the same ol' thing all the time, "BUT", in some cases, if you do not meet minimum codes for your community, problems can come back to haunt you.
Personally, I doubt if you will ever have a problem because most communities do not require a building permit for such work, therefore, my friend, no one will ever know if you are in violation, if indeed you are. But, if you are in violation cuz the code requires more ceiling height for occupied spaces, and you have a problem and someone gets hurt, you are open for trouble.
Also, don't count on this being a selling point cuz a realtor will have to disclose the issue.
Now, that all said, heed Henry's advise, add to that some precaution with any obstructions over door ways and you are on your way. I might add that if you wish, you could still suspend a grid ceiling, but you might have to add some furring strips to the existing subfloor and attach the hangers to that and placing the "T"s as close to the floor joists as possible. This would leave you with a totally accessible area under your floor for when you need to get into things later on.