It will be best if you first decide which places you want to visit in Himachal, and visit the HP Tourism office. I have been to Himachal, and let me tell you that the HP Tourism Hotels are located in the BEST locations, and rooms can booked from Delhi and Chandigarh. It is always better to hire 4 WD like Scorpio/ Sierra etc, since this will give you the freedom to travel at your own pace and time, and see many off beat places also. Check the HP tourism website. http://himachaltourism.nic.in/
To cover Himachal at one go, you will need to plan a longish holiday. You can instead, select one or two district, and cover it through 8- 10 days. The Shimla- Naldehra- Fagu- Narkanda- Sarahan circuit can be covered in 8 days, with detours to Tattapani , Chail, Juggal and Hatkoti. This area is ABSOLUTELY GREEN and beautiful, with views of Shrikhand Mahadev peak and Kinner Kailash Peak. You can also try going upto Sangla/ Baspa.
Tour operators always OVER Charge you. If you dont want to travel by car/ jeep, you can try the HP Buses to all these places. You will even find luxury buses on these routes. Have a nice holiday!