I seem to be facing the same issue here, I can't judge the size of the market, its even more complicated because the market depends entirely on geographical location. Am thinking of locating in trendy, up and coming areas of town, but am confused...young student areas or yuppie newly gentrified areas? or largely immigrant ethnically mixed areas?...... once again any suggestions?
As for location, you should definitely need to choose a place with a greater circulation of people, and also that place is under video surveillance, you certainly don't want someone to steal or break your ATM. A logical choice would be a mall, because nowadays people spend a lot of time in such places, and there you will certainly cover all age/ethnic groups.
It would be wise to do some research into how much people are interested in such a service at all, and of course keep an eye on other crypto ATMs nearby. What you can do to attract potential customers is lower fee on your service, and support by phone or e-mail - people will certainly appreciate such things and come back again.