Certainly feasible, although as you remark, quite a tall order for your first project. Obviously though, you don't have to do it all at once. Depending on your sensors and the layout of your place, it might make sense to use more than one arduino - to avoid long wire runs or if you run out of I/O pins. How do you plan to communicate with the Pi? xBee, ethernet, wifi, cheap radios?
Take a look at this site - lots of relevant examples: http://www.desert-home.com/.
I'd have the Pi run a web server for your smartphone needs and keep a mysql database with your records and current threshold settings. I'd let the Arduino(s) manage their own affairs, just checking in with the Pi periodically to send sensor data and to find out whether their threshold data had been updated.