Hello Uncle H and welcome to Mac-Help.
First off, I'm honored to meet someone with 4 MobileMe accounts!

I was around back in the day when MobileMe was .Mac!
I'll do my best answer your questions as simply as I can.
To answer your first question: You can transition all 4 of your .me accounts to iCloud. Just follow these instructions here:
Transitioning From MobileMe to iCloud. Unfortunately, you will only be able to use one iCloud account at a time for most iCloud services on your Mac. You might be able to use more than one iCloud account for email at a time, but I can't be certain for sure. My best guess is from having poked around in system preferences, you can't.
What I would do is use one of your iCloud accounts, once you transition from MobileMe, as your primary account that you setup on your Mac, iPhone, and iPad and use that for all your syncing needs so you're iCloud email, contacts, calendars, etc are accessible on all your iDevices. If you have contacts, calendars, etc on your other 3 accounts and you want / need them to sync across all your devices as well, I'd say add them to your primary iCloud account. Then I would just separate them so you can distinguish friends contacts from work contacts and work calendar stuff from friend calendar stuff. You can do that by creating groups inside your Mac's Address book program. Create on group for family, friends, work, etc. And you can do the same in calendars too.
Here's what I would do if I was in your position:
1. Get a new Mac with Lion installed on it.
2. Setup the new computer the way you like it.
3. Once Lion is setup, use the above link as a guide and transition all your MobileMe accounts to iCloud.
4. Now pick one of your iCloud accounts to use as your primary and enter in that information into the iCloud sections of your Mac, iPhone, iPad.
5. Make sure that all your iCloud settings / options on each of your devices are turned on.
6. Open up your Mac's Address Book, iCal, etc and create some Address Book groups and some different calendars to distinguish friends from work, etc.
7. Open up Safari and log into one of your non primary iCloud accounts and look at your address book and calendars.
8. Manually type what you see on Safari into your Mac's address book and calendars.
9. Once that's completed, log out of your iCloud account on Safari.
10. Repeat steps 7 - 9 for each of your non primary iCloud accounts. (Depending how much info you have on your non primary accounts, this can take a lot of time).
11. You should now be all set.
I know you still want to send/receive email from your other iCloud accounts. You'll probably need to stick to using the website to read and send emails from your non primary iCloud accounts.
As for your other 3 accounts, you can transition them to iCloud from .me, but you'll only be able to use one at a time.
I hope that all makes sense. There's a lot of information there. And sadly, you have to have OS X 10.7 Lion to take advantage of all iCloud services. So DO NOT transition to iCloud until you have a new computer with Lion up and running! And yes, .me will be discontinued as of June 2012. I am not sure what will happen if you don't transition to iCloud after that date.
Anyway, I hope that all helps. Please feel free to ask more questions and someone here will do their best to answer.
Cheers
Searay