good luck there are some really nice people here willing to give you the BEST advice!
Lol, your dad's not old Katling - he's the same age as me
There aren't that many versions of the Riva 510 - some just have larger capacity batteries - the higher the mAh rating, the longer they will last before needing to be recharged. As for Kanger & Boge, they are different makes of cartomisers.
If you buy a Riva 50 kit that comes with atomisers, you can use cartomisers with it - more or less anything that has a 510 thread will fit. Cartomisers hold more e-liquid than the cartridges that you use with atomisers.
A 10ml bottle of e-liquid would only last him about 4 to 5 days. I would say he would need a medium to high strength (18 -24 mg). I've tried several of Paradise Vapes tobacco flavours & liked them all -
E-Juice - Tobacco - Paradise Vape UK _ Vape dont smoke