Good to hear that you're already enjoying it... I hear ya.. about possibly over thinking it... That sounds exactly like what I tend to do... lol...
My rule of thumb is when it comes to estimating calories that I'm eating is to err on the high side... and when estimating calories burned from exercising to err on the low side....
Enjoy the fuel band... Have fun with it... And I'm sure with a little trial and error you won't be overestimating your deficit... And if you're losing weight than you'll know you're not