How about several modules in a single installation?

Hello there,
I already have a Drupal installation and I´m doing just fine with it.
My site´s only for specific target, so it doesn´t receive much traffic as... may I say Drupal.org or theonion.com

But, we´re using our site to allocate our "daily weblog" (in a manner of speak in), our OnLine Courses, and the "online tail" of our brick and mortar courses.

So we´ve already installed several modules:

attachment
casetracker
devel
excerpt
filemanager
flexinode
gsitemap
image
img_assist
logintoboggan
paging
print
search_config
tac_lite
userplus
views
webform

Besides that, we have some more active modules that came inside Drupal´s core.

Now we want to add inside this one site our "alumni" area, who is going to need even more modules:
buddylist
flag_content
profile_pages
profile_visit
subscriptions
user_readonly

And maybe a few more. I´ve already tested those ones, and seems to work exactly as I wanted.
(I´s easier for us to use this way instead the OG modules).

My question here is: Should I put all those new modules in a different Drupal installation? Are there known issues about installing several modules? Can all crash in at anytime?

I wanted to use the same installation, to get a single username´s database, so once the student´s get their diplomma, they are going to be changed to the "alumni" role a lot easier, withouth the need of creating a new user somewhere else.

It would be nice to use a subdomain also, something like alumni.oursite.com (In that case I would need another installation in the subdomain, I think)

I just want to find the easiest, effortless way for teachers to work with, but don´t want the site to get "messy".

I´m really a bit clueless about this, I would really really love to read you thoughts and experiences about this issue.

Thanks in advance!!!

Rosamunda
Buenos Aires | Argentina
www.ligadelconsorcista.org