Just different preferences based on the advantages and disadvantages of one
MDE or two MDEs as specified in first post. To add a person to your reservation/package, you'd have to call Disney. You can't do that on your MDE. You can only add profiles.
If you buy the tickets online, you'll select which profiles you want them associated with at the time of purchase.
You can take vouchers to a guest services window at a park, resort, or Disney Springs and ask to trade in for a card. The reason a guest might choose to ask for cards would be that the guests who will be using the tickets don't have MagicBands with which to access the party entitlements. In other words, there is nothing wrong or suspicious, etc. about you asking for cards.
Your name and ID will match the name of the purchaser on record. A guest might buy four party tickets for four friends with different surnames. It doesn't matter that his name is different, when he takes the voucher to trade it for cards. However - it might be worth paying to have the cards mailed just for the peace of mind. You won't have to think about the visit to guest services and possibly fretting about something going wrong. If you'll fret, then pay. If you can make up your mind not to fret, then wait. Personal preference.
Nothing has changed. This is just personal preference. A CM might make a joke or ask a question about your phantom names if they sound eccentric. This doesn't bother me. Does the possibility bother you? If so, give them boring names.
They're not looking at names - just confirming that the entitlement is present. But again, if the possibility of having the names remarked upon gives you the willies, stick with quotidian names.
No need to reassign in your case. Unless you suddenly realized you had lost the plastic cards. You could just reassign them to your real profiles and enter with your MagicBands. Not that you are likely to lose the cards.
Each person should have a band with them at all times so that you won't miss a ride photo. Memory Maker works independently of admission media, regardless of whether you have party tickets, etc.
You can only prebook FP for the party day in the MK for the cards. But you can use the cards at any kiosk in any park for SDFP.