Can't help you with the weight but as regarding projection. Within the UK a rear projection of 1 metre or under does not need to be marked between 1 & 2 metres it needs to be made visible and above 2 metres it needs a marker board see
Transports Friend - Abnormal Load Projection I can't imagine you will be needing a marker unless you mount it lengthways. I'll leave others to tell you whether you need a plastic or alloy square board dependent on where in Europe you are going or you may find the info by looking at previous threads.
Newbie to motorhomes, scooters or both? I'm presuming both.
What will be best depends a lot on what you want. My one golden rule would be
DO NOT BUY A MOPED even if you are 5' 1" and weigh 7 stone you will be limited to just over 30mph. You tend to become gutter trash and vulnerable , then with any road with over a 30 limit becoming positively frightening. If you are of any size or weight these machines while never being funny become even less so. Though some do ride these and are happy so what do I know. If you passed your car test before 1st Feb 2001 this is the only thing you can ride without taking a CBT. It's not worth it because as said previously mopeds are horrendous and even the worst CBT is better than no training.
Scooters come in all shapes and sizes. I'm really a motorcyclist so we have one or two issues with the small wheels being less gyroscopically stable and the fact that your feet are in front but as a newbie you won't know any better sorry different and all will be good.
See if you can get a free 1 hour or 2 hour taster at any training centre before your CBT. The bad bit is at the end of two hours you may well be thinking this is not for you, "I'm not confident with this", "I don't like this" or just "Help mummy" This is normal, man up! The advantage is if you have done this once or better still as a major freeloader 2 or more times it prepares you for your CBT. The CBT is not a test but a certificate of basic training at the end of it you should be confident (ish) and have certain basic skills and knowledge. It is not supposed to be time sensitive if there are issues it should not be problem for you to come back the next day.... and the ne..... In reality it's priced cheaply and you ain't going to be confident within a day. Some advocate doing a full direct access all in one. I've seen some former Direct Access riders who bought 600s as a first bike and just intimidated themselves. You only want a scooter so Direct Access might be suitable but six months bike time before a test makes the test far easier.
The smallest lightest scooter will be easiest to load on the camper but super scooters are very practical with spaces for shopping and an open face helmet sometimes even space for a full face one.
There will be a range of power outputs, up to 15BHP on an L plate is legal and scooters with close to this power output being quite useful. It will take a passenger once you have passed your test.
It might sound helpful to say to try a CBT centre with a few different bikes so you can see what you like but unless you are a prodigious talent you wouldn't be able to judge.
For a first scooter I'd buy something cheap enough to able to throw it down the road. That doesn't sound positive does it? It's still true though. Also 125's are the biggest bikes you can still buy as 2 strokes as against 4 strokes. 2 strokes are a lot more easy and tractable to ride as small single cylinder bikes but you will get by with whatever.
Though I said buy cheap don't buy a Chinese bike unless someone who really knows their stuff knows a good one. They are generally carp with no spares backup.