elemmac
Angel Diva
I would start out by talking to a local bike shop (or two...or three...), tell them your story, pretty much exactly what you put in your first post. What your background is with road biking, what you want to get out of this bike, where you want to take the bike and what your budget is. They will give you some suggestions based on what they carry in stock, which is why I'd say to go to two different shops, just to get a feel of what brands there are available in your area.
For your first MTB bike, I wouldn't be super worried about demoing...but DEFINITELY try bikes at the shop. Just like buying a car, you wouldn't do it without taking a test drive. They'll generally let you take it for a spin around their parking lot, up the road, or in other designated areas. This will give you a feel for how the bike fits, and you'll be able to feel the differences between bikes and brands. Try going a bit faster, slower, tight turns, long turns, etc. really get a feel for how the bike is going to handle.
In my opinion, starting out with a fairly basic hardtail for your first mountain bike is a good way start out. You don't have to think about locking out suspension on your climbs, you don't have to think about when to drop your seat post...you just focus on riding, staying on your bike, and learning about things that you like/don't like. After you start to get a feel of the terrain you like and want to ride more of, then consider upgrading components or selling the hardtail and buying a full suspension. Maybe you end up liking climbs, smooth trails and want to stay with a hardtail. Or you'll start to enjoy downhills more and want to move to a full suspension.
^This is how I started out, and actually sounds like @Albertan ski girl and @SallyCat started out in similar fashion.
For your first MTB bike, I wouldn't be super worried about demoing...but DEFINITELY try bikes at the shop. Just like buying a car, you wouldn't do it without taking a test drive. They'll generally let you take it for a spin around their parking lot, up the road, or in other designated areas. This will give you a feel for how the bike fits, and you'll be able to feel the differences between bikes and brands. Try going a bit faster, slower, tight turns, long turns, etc. really get a feel for how the bike is going to handle.
In my opinion, starting out with a fairly basic hardtail for your first mountain bike is a good way start out. You don't have to think about locking out suspension on your climbs, you don't have to think about when to drop your seat post...you just focus on riding, staying on your bike, and learning about things that you like/don't like. After you start to get a feel of the terrain you like and want to ride more of, then consider upgrading components or selling the hardtail and buying a full suspension. Maybe you end up liking climbs, smooth trails and want to stay with a hardtail. Or you'll start to enjoy downhills more and want to move to a full suspension.
^This is how I started out, and actually sounds like @Albertan ski girl and @SallyCat started out in similar fashion.