I'm buying this house and the 100amp service wires coming from the meter, going to the main breaker box had been cut.. which left it 3ft shorter. My question is can run the service wires to a small panel, and just add the 3ft going from the panel to main breaker box..
The wires you're talking about are service wires, and they have two very important properties that rhyme with "don't mess with them". First, they are always energized - unless the service drop is removed at the pole, or the meter is pulled. Second, they are totally unfused - it can arc very destructively because there is no circuit breaker to stop it.
As such, the service entrance cable run from the meter to the first breaker (e.g. main panel) is very tightly regulated - it must be protected and it can't go far.
In NEC 2020, this problem was eliminated altogether. Under the NEC 2020 rules, you must have a main breaker outside at the meter. This protects the wires you are referring to.
The NEC 2020 requirement sounds a bit like what you are proposing to do, except I gather you are not aiming to put the main breaker outdoors.
Maybe you should, if the wire length allows. Or even if not, wire isn't that expensive. The important part is to use aluminum wire, which is far less costly and performs just as well in these large sizes. Terminals on the meter pan, main breakers and panels are all rated for aluminum (made of aluminum).