Did you by this new one to hunt with primarily or just lots of target shootin. The amount of shooting and primary purpose really do play an important role. I wax my string when ever i forget the last time I did it unless I notice the strings looking like it needs it before I forget. Todays high quality strings should last a good long time depending on how much shooting you do, if you are worried about string life find a sport shop guy, that you can trust to not simply want to sell you more stuff, and have him inspect your xbow before and after your archery season. Your choice of arrow selection really comes down to you just being consistant in your shooting and any good arrow put in the right spot will do the job, your quad400 is plenty strong. As for the trigger and safety don't over oil them. I hope it helps