Could you help me out with plugins needed for a site idea?

Hey guys!
I got an idea for a new site, but I'm unsure which WMPUDev or other party plugins I should use. I'll try to explain how I would like this to work, though it may be hard to imagine.
- Multisite will be used for multiple registrations
- Custom post types will be used (the WPMU plugin looks to be exactly what I need)
- Most of what the registered use does will be done in the admin
- Admin will be very custom, a couple WPMU plugins I have looked at are also great for this

Once the user logs in, you'll see only a couple menu items in the left menu (custom post types). One will be Your Gardens (for example). You'll start off by adding a new garden with some basic info (Garden 1). After saving this garden, you should be able to click this garden and possibly a secondary left menu will show up, which will have tabs for Water consumption, Flowers, Pictures.
Another custom post type will be Water consumption. You can add a new watering event and the consupmtion of water (remember, this is just for examples sake). But you should be able to choose which garden this event took place in. In other words, if you go back to the Your Gardens menu and open Garden 1, you'll see all water consumptions that are related to this garden.
Water consumption is in there "twice" because you may want to show the consumptions for just that one garden, or all the consumptions for all gardens.

The user should also be able to make this information public on his/her sub-site frontend.

Is something like this possible?
I've seen a similar structure before, but I can't remember where, and I think it was built with Wordpress, although I'm not sure.
Any input is much appreciated!