NEWB here!!

Hey all! New to the site and fairly new to swimming in general. I live in Florida so I've known how to swim my whole life, but I've just recently (beginning of the year) started swimming recrationally/for excersize. I'm seeking commision in the US Navy; so I'm trying to stay fit. I've been swimming freestyle now for a few months and for the last few weeks with goggles and a snorkle. Before starting freestyle, I did *** stroke (my verison) and side stroke (Navy's version). No matter what I do I seem to swim about 2 minutes per 100m freestyle. How is that timing for this type of swimming? I even used a pull bouy and it didn't slow me down that much, albeit I was much more tired at the end of the swim. I usually swim 500 to 800 meters every few days on my lunch break. I even did 1000m last week. Felt very accomplished that day. Also, I'm going to start training for an upcoming sprint triathlon. I have about 5 months to train and I have a plan of attack, but I'm trying to learn more about open water swimming. At what point should I attempt an OWS? What should I practice before actually attempting an OWS? The sprint tri OWS is between 400 and 500 m. Should I pratice this distance open water or more? Thanks for listening and I hope to learn more. Dave