The lenses will fit but will not autofocus as the D3100 does not have an in-camera focus motor and requires AF-S lenses for auto focus.
If you wish to use AF with your lenses, then you should consider the D7000 or a model with 1 to 3 numbers in its name (D300S, D700, D90, D3S, etc).
Note that the angle-of-view of your lenses will be different if you do not go with a full-frame body (D3S, D3X or D700). So a 70-210mm lens will give you the equivalent angle-of-view of a 105-315mm lens on your film camera. You have to multiple by 1.5 which is called the focal-length multiplier.
The flash will probably work, but I'm just guessing!