I'd second the recommendation about Hyphalon over PVC.
For best portability, consider a 2-3hp and a dinghy style that rolls up completely. I had an Avon for years with a 2HP Honda and stowed it in a lazarette in a Catalina 25. After a long cruise, it could be pulled out and launched in 10 minutes.
If you want to consider deck storage, most Zodiacs are at a disadvantage. West Marine, Achilles, Avon and many others have three air chambers for the hull (plus the inflatable keel); you can deflate just the bow and lash down a smaller package on deck. Most Zodiacs have a port and starboard chamber eliminating the option to shorten through partial deflation.
I've used 2, 4, 6 and a 7.5 on various inflatables. Size is determined by how you are going to use the dinghy. If you have to travel more than a few hundred yards out to a mooring or will take the dinghy in tow when coastal cruising, the littlest motors (including electrics) have some limitations. But, the little ones can be removed and rail stowed without a davit/hoist.
I currently have a 7.5 and like the ability to really scoot when solo and still plane with two aboard. This next season is my first with this combination and, having no davit/hoist, I'll need to keep it on the transom and tow the dinghy when cruising.
Oars only can have some serious limitations. You don't want to venture very far from your mooring and need to be very cautious when cruising. Inflatables don't row well (they don't carry the momentum of the oar thrust) and wind, current and tide can sometimes prevent you from getting to or from where you want to go.
You'll have oars on any of your choices. Use them as much as practicable, yeah. But be careful about having no outboard.
A good electric trolling motor is an excellent choice; you can buy inexpensive solar panels that will keep the battery topped off.
Here's some more information you may find handy.
Dinghy selection overview
Hull type selection
Hull material and floors