Steel or Aluminum

Personally I like a cruiser frame, but a more modern one- not old heavy pig iron with a big sweep of a downtube.. I've built two Huffy frames up- not terribly new, but fairly light oversized tubes, and a Micargi- also more modern with oversized tubes-

Used to race USCF 14 years in my crazy days and was a bike mechanic among other less mentionable things

A cruiser frame has the better clearances for the chain and the tank- I'd use a steel diamond frame otherwise, but the tank is in the way of peddling much, and I bulld a bike with light alloy rims and narrow tires to peddle shut down as well as roll easy for the motor- I never use a chain tensioner, and match the two chains up otherwise- saves much weight and has been very reliable.

so yes, I recommend alloy rims myself- 700 c and probably about 32mm wide for less experienced- non-cyclist riders

Two stroke China Girl is the most practical but 4 strokes are reliable and quiet if you're good with mechanics.

a lot of the choice depends on opinion of the builder - aluminum is nice for smoothing vibration, but tends to crack after a year or so of hard riding

I like steel cruisers mostly because I'm almost 70 & can't bend far enough to ride a mtn bike & I want the strongest, heaviest frame I can get to have a chance of surviving the huge potholes around here.

I prefer steel because it can be welded for repairs or modifications like adding in mounting tabs or extra gussets to further strengthen the frame. Aluminum can also be welded but would need to be heat treated again or it will lose a lot of its strength... Aluminum alloys like 6061T6 are heat treated in order to enhance hardness and steength, the 2 series along with the 7 series alloys can't be welded but the 5 and 6 series alloys are easily welded. The T number at the end is the heat treatment process to give it better hardness and strength properties. 6061 is very popular for its excellent balance of strength and corrosion resistance.
7075 T6 is both harder and stronger than mild steel but needs to be protected from corrosion and will crumble to ash if welding is attempted. 2024 T3 is also very hard and strong but will oxidize if not protected by painting and will also tend to turn to an ashy mess if trying to weld or melt. 6061 isn't as strong or hard as 2024 or 7075 but it's almost as strong as mild steel and weldable, it does need to be heat treated after welding is done tho or it will be very soft at and near the welds.

Did you find out what is in the box? 2 stroke? 4 stroke? fricton kit?