Don't worry about "acceptable" or "protocol," worry about what's comfortable for you!!!

For short transportation rides around town on my hybrid, I just wear whatever I'm wearing. Over my street clothes I'll throw a high visibility jacket (with or without the removable sleeves) with my garage door opener in the pocket. That bike has saddlebags, and I'll normally want to be carrying a purse plus whatever else I need to/from my destination (yoga gear, grocery bags, binoculars, etc) so I don't need more pockets in my clothes.

For recreational road rides I wear a jersey just because I need pockets for my phone/ID and little stuff like eyedrops and spare chamois lube - and also because I sweat and cotton turns to a sodden chafe-y mess.

I always wear sleeves, partly as a holdover from my racing days (ancient history now) and partly for sun protection.

How many to buy - how often do you ride and how often do you want to wash your jerseys? (They'll last longer if you wash them on gentle cycle or by hand, no fabric softeners, and definitely air dry.)

As far as brand - if you have a LBS where you can try them on, buy the brand(s) that fit! If you order from TE, the staff knows their product line very, very well, and if there's something they don't know off the top of their head, they'll pull a product out of the package and answer any questions you have! You can call or email and they're really great about answering questions about proportions, sizing, pocket size, zippers and seams, anything you might want to know about a garment, and they're great about returns also if you order something that doesn't work for you.