your service provider can also provide information on aproximately where u are (base on the line setup). but it won't be exact. have u used google map without gps on? what will happen is google maps will give u a approximate circle on where u are. and that circle radius can be pretty big. and coz of that, the direction navigator won't work. basically u just will know where u approximately are, and that's it. no other gps service can be used.

Given the bolded part, opt for the Wi-Fi + Cellular model.

Go for 4G version, u'll never regret.
Go for without WiFi ONLY version, still not too bad, but u might face regretting issue in future. Maybe won't.

My ipad2 3G serve me well with the GPS chip when i'm in Thailand for 10 days holiday.

Bro
If ur major purpose of using ipad is internet and navigating save on the size,, go for 16gb enough already