The device requirements look about OK to me, and if they look about OK now, they'll be a complete non-issue in two or three years. Design for the future! Regarding databases, my impression is that server resources (both computation and storage + traffic) are quite cheap these days, and if the data doesn't change often, you only pay for computation time you need. So, if Martin can provide servers that's good, if not, it shouldn't be a problem either. You should be able to collect server fees as donations, or maybe charge for the app if that's one day possible. So, if the results are good, I'd say go for it. I'm not likely to use offline maps myself though, with or without this change, as online is not a problem for me. But, if I did, I'd want to use something that works.