Upgrading Drupal

I'm not really sure what's going on here. I have a Drupal 4.6.5 multisite installation with some shared tables, but I'm looking at upgrading to 4.7. Why? Because there are some new modules, and more importantly, improved/fixed versions of other modules that only work with 4.7, and that functionality is important to me. But I have a couple questions:

1. How different IS 4.7? Complete re-write? How backwards-compatible is it with modules that were written for 4.6.x and haven't been developed for 4.7? If it's completely different and none of the old modules will work... is this going to happen with every bloody release? I used to use PHP-Nuke and while a couple version upgrades broke some modules, the vast majority of modules still worked when a new version came out. Themes likewise.
2. What on earth is with the different versions? What is the difference between 4.7.0-beta.x, 4.7.x, and CVS? I thought software tended to have the-stable-version-that-is-released, and the-unstable-version-that-is-coming. But Drupal seems to have at least 5 different versions available for download, and a hodge-podge of modules for each. Will a CVS module work with, say, 4.7.x?
3. Am I going to have a lot of trouble updating all my database tables with my multisite shared-table installation?

It's all very confusing. It would be nice if someone could clear this up. If there is a page in the handbook about all this, I couldn't find it. There should be. Something like:

I installed the DRUPAL-SA-2006-001 security patch this morning to my 4.6.5 site. When the menu cache was regenerated this evening, some of my menu items disappeared. I temporarily disabled menu caching, and rolled back the patch, and the menus reappeared.

I see that the patch removed a bit of code that set this "access" variable to true for items that were "MENU_CREATED_BY_ADMIN". I assume that the patch is doing the right thing, so I'm assuming that my menus were somehow misconfigured to be admin menus. But, I can't, for the life of me, figure out where this setting might be.

Is it possible to find out the current version of my drupal install without the changelog.txt

Ok, I think i deleted my changelog.txt, now I am not sure my version of drupal I had installed. Is there an alternative way to find out?

I have not been able to successfully upgrade a Site5 Fantastico (scripted install) drupal 4.6.5 intall to a 4.7 beta6 install. I have a request into site5 to find out if their Fantastico version has any unique characteristics that would make this a problem. However it is likely I am simply not understanding something clearly regarding the upgrade process. I have searched this site and read the upgrade instructions.

I've restored a data backup on my site and found a rare behavior with the characters Á and Í: all ran out.
When I try to send them, I can see them in preview mode, but when upped, they dissapear.
¿Anybody knows what's the matter?

Not feeling particularily adventerous, I thought I'd ask before going ahead.

I found instructions for how to upgrade from 4.6.3 to 4.6.6 and was wondering if it's the same route to take from 4.6.2? Or must I take an additional step between 4.6.2 up to 4.6.3 before following those instructions?

I apparantly missed something along the way, by ways of security patches and whatnot... *kicking herself* Thanks for any advice you can offer up!