Dave, the FlightStream 110/210 are for the older Garmins. On the 750, you want the 510 which is just an SD card with built-in WiFi and fancy software. Makes installation very quick and easy in comparison to the 110/210 though!
There is no direct subscription for the 510. When I bought mine (granted, 5 years ago) it was $1,495 for the card, and installation is pretty trivial so should be no more than an hour or two at your avionics shop rate.
All the features of the 510 are usable with both Garmin Pilot and ForeFlight except Database Concierge which is Garmin Pilot only. I use ForeFlight, but I have to pay $99/year for the basic Garmin Pilot subscription (grrrr). The PilotPak for databases comes with an "upgrade" from the basic Garmin Pilot subscription to the next level up, but does not come with the basic subscription.
If you don't want to use Database Concierge, you likely don't need any subscriptions you don't already have, unless you're one of those weirdos that doesn't use one of the two biggest EFBs.