No. 4 Magazines

Greetings gentlemen, I am new to this forum but not new to guns, rifles in particular as I was in the marines when the first space shuttle blew up (dating myself) but I am new to the enfield club having just been given one by a friend who upon moving into a house he bought found the rifle rat holed away somewhere and didn’t want it and knowing that am somewhat of a rifle buff gave it to me. I don’t know much about the rifle however I do know that the wrist ring has a date of 1904 on it and the barrel and the receiver serial numbers match... oh and the riflings and chamber look as though they were cut yesterday. Alas, it has been sporterized  but to what extent I know not, I would like to start shooting it but would like to do so safely, also it is missing the magazine. I understand that the no.1 and later rifles have different mags, can someone please let me know what to check on the action for possible problems, troubles, where I can get the correct magazine for my rifle and some safe starting loads, I have Hornady 150 gr. Soft points also some 123 gr. Bullets that I understand will shoot well enough For plinking. Reading your posts I can see that many of you know allot about these wonderful pieces of history, anything will be greatly appreciated. Thanks.