See the thread "Lake Spring Hetch Hetchy Backpack" at
http://www.yosemite.ca.us/forum/viewtopic.php?t=242
It's looking better for May with the lack of snow (in fact the lowest level for 20 years). April is still early. You'll probably see hard-packed snow at the top of Smith Peak, since my map shows it at 7751'
Rancheria Falls is clear right now--it's only 5000' or so. It also has the advantage of facing south, so it gets a lot of sun. Above 6000' or so, expect snow (just an estimate, since it's not mid-April yet).
I don't think you need crampons. Snow shoes will help you from punching through when the snow gets soft late in the day.
The HH road is clear. There's nothing on the Hetch Hetchy Road as far as a town or store, especially this time of year. You can pick up food and gas at Groveland on Highway 120. Top off your gas tank!