Is Drupal Right for me in this particular proyect?

Hello,
I´m sort of new here at Drupal, but I´ve already tested it, and found it amazing.
I´m working in a web application that wants to administrate apartaments [and maybe car´s] rents.
Now, I´ve searched the forums, but still don´t know if Drupal can manage the following:

#1. Create accounts for people that has several apartments to administrate. Those apartments usually are form separate owners, and have obviously different tenant´s.
I want tenat´s and owners aswell to be able to communicate with the administrators, and sort of control what they are doing [so they could actually see all stuff that´s going on]. I think that OG can help with that and some sort of taxonomy control per user.

#2. Manage administrator´s accountability (this is the most important stuff that I cannot really know if Drupal can handle). I want they to manage each single apartament´s accounts:
Knowing what aumont each tenant is paying per month, and if they are late in their payments to add an interest rate (wich could be different in each case, because some contracts could apply 1% of monthy interest rate where others apply 2% or 3%). Maybe some contracts could even apply different ways of calculating interest rates).
Some contracts could add a fee to be applied in some cases, or some extra charges, that should be calculated too, with the possibility to add or take off certain items.

#3. The application should permit each administrator to have n number of accounts, and to have n number of administrators, so it should be scalable. I think Drupal doesn´t have a problem here.

#4. According to the legislation of each country, it could be other items to consider for the final sum of each tenant to pay, so each month could be a different sum to pay, for each apartment, a different calculation.

Now, I´ve thought largely about the database and language to apply to this, and finally decided that MySQL and PHP are the better ones.

My issues begins when I decide to start with raw PHP and writting the application by hand, or using a framework, like Zend or Symfony (or maybe don´t using PHP at all and use python because Django seems excellent).
I think that I don´t have to reinvent the weel here, so, maybe using a framework could be better.

I consider Drupal as a framework and not as a CMS application. And I like it very much.
I know that there aren´t contributed modules that can do all that I´ve named, BUT, I would like to know if Drupal can support something like this in case I decided to create a module from scratch.

One thing that I have to put into consideration, besides the limitations of using a framework in the first place, is the Drupal versioning.

Am I going to put a lot of work into something that next year cannot work under Drupal 7? (or 8, or whatever). How can I manage my own versioning when Drupal changes so often? I´m just starting to understand Drupal 5 with the excellent Pro Drupal Development book, when Drupal 6 caes out and changes A LOT of things!

Hope to hear you thoughts about this!

THANKS!!!!!

Anita