The vehicle can handle a maximum of 7400W, or 32A maximum current, whichever is larger. Electrical code in the USA calls for not loading the circuit for more than 80%, so a 40A circuit could handle a maximum of 32A EVSE, and a 50A circuit can handle 40A one. Yes, wire is probably a significant portion of the cost as will the labor for a long run.
IF you choose to use a unit with a plug, make sure than when you insert it, it is tight. If it doesn't take much pressure to insert it, the contacts are worn out, and things could overheat, melt, and possibly start a fire. There's usually no good reason to set the vehicle to less than maximum unless where you're plugging it in is shared with some other load and the combination might trip the breaker. Having a large EVSE won't overload the vehicle.
FWIW, on a CCS (dc high voltage charge), the i3 can handle up to 50Kw input, and the input voltage will be somewhere between 360-380 vdc or so, depending on where the batteries are in their charge cycle. When using acv (an EVSE), it can handle much less input power.
2014 i3 BEV, 2021 X5 45e
(The i3 will be sold soon, <17K-miles, interested?)