It's actually a 4th Model (according to SCSW #3). 3rd Models ended at serial 322,700. Only differences were internal. It's also a pre-1899 gun, meaning it's exempt from FFL-BATF requirements. There's a slight premium for that due to lack of red tape to buy-sell. (prior to 382022 are considered antique). That being said, your gun was made between 1895 and 1898. If you wanted an exact date, you would have to get a factory letter.
As for price, if you got it for $40, you did great. I would say book value for that condition is around $150. The last shooter I bought like that cost me $100.
For the DA locking problem, there's a good chance that a good disassembly and cleaning will correct the problem. I'm sure there's 110+ years of crud inside. Take it apart, clean everything, and lightly lube it.
I shoot mine (over a dozen various top breaks) with light loads or black powder. As long as you can get it locking up, it won't hurt to shoot it.
Hope this answers all your questions,
Chris