Hi,
its not that bad, my installation is a mish-mash of different revisions of stuff that have been in place since V6.
the database structure has stayed the same (mostly) throughout and any changes in it were additions.
As for the modules, your old ones should work fine (mine did), I however first ran the following things before testing this last weekend
I already had a emoncmsTesting folder, however to create one (assuming linux)
cd /var/www/html
cp emoncms emoncmsTesting
this creates the emoncmsTesting folder, with the contents of the old installation of emoncms
I then did a git pull which updated the base install of emoncms to the latest.
git pull
Finally I then moved into the Modules folder
cd Modules
Moved the dashboard and app folder out of the way, I moved to my home folder, but anywhere out of the installation will be fine.
mv dashboard /home/pi/
mv app /home/pi/
Then did a git clone of the new modules
git clone https://github.com/emoncms/dashboard.git
git clone https://github.com/emoncms/app.git
I now test emoncmsTesting and then once happy, will move the old emoncms out of the way, and the testing into the new one
mv emoncms emoncms.old && cp emoncmsTesting emoncms
This is how mine went, yours should be similar, but back it all up first is my best advice
Jimmy