I read depth, speed and water temp. I plan on adding wind speed and direction. Someday.
The stuff I have now is old Datamarine... which means no replacement parts except maybe DMI.
I am looking at Raymarine ST60 series.
Interestedly, I am having some battery issues right now (probably need to replace them) and have been sailing with the batteries turned off, thus no instruments... the boat seems to move just fine. (GRIN) Of course those new telltales on the sails do help.
Regarding your water temp... I know that when my instruments read close to 68* then the water is fine. GRIN