Centrally located near a well known tourist site Galata Towers. Ten minutes walking distance from tram and water taxi/cruise stations. Literally 10 minutes walk to the start of the famous İstiklal street that leads to Taksim square and spice bazaar. A short inexpensive tram ride to the Blue Mosque, Ayasofia (Hagia Sofia), Topkapi and grand bazaar.
Suggest you buy an Istanbul Transit Card cost of which is 6 TL (5 of which are refundable upon return) and add TL to it as for use. More than one person can use the same card.
I bought a local SIM from Sultanahmet for 150 TL (10GB data, 300 local calls and 500 SMS). This is more expensive at the airport.
Change money outside the airport arrivals lounge for better rates. Rates are still a bit better in the city.