Frank, the best time to catch DV's offerings is late Feb through March. Daytime temps are mild in the valley - 70s to 80s versus 120s in the summer - and the air is super clear, without that heat-haze you constantly see from May to September. Temps up high and at night are not bad at all - low 30s are the worst I've experienced in 7 years of tripping out there that time of year. It's a totally different park when the heat is gone, and an under-appreciated gem.
Telescope can be done in early spring, but it's very, very dangerous most years. The final ridge to the summit, which is just a class 1 huffer in the summer, is narrow, steep, and precipitous. It tends to be glazed with ice and even experienced winter mountaineers die there. Climbing Telescope safely is best done when the snow/ice is mostly off the trail - May to October. Wildrose Peak, 2000 feet lower, is a much better bet in late winter/early spring and affords mostly the same views. Our plans for Telescope are tentatively based on what beta we can get just prior: any ice reported, and we go to Plan B.
Telescope/Bennett/Rogers and Wildrose are the only two maintained alpine trails in the park. All of the many other peaks are accessed by use trails or class 2-4 routes. There are a zillion good canyon hikes in the park if you enjoy that.
If you don't camp, you have extremely limited options. There are two lodging facilities at Furnace Creek and a small one at Stovepipe Wells. Just like gas in the park, though, they are very pricey.
