Hi Ronna,
to answer your questions - no, you don't need a visa. As for the best time for coming to Israel, I'd say it's between late February to July, and between early september to November. You should note though, that prices in hotels are at their peak duting Jewish holidays, which this year come April 19th-26th (Passover), and Sept. 29th thru Oct. 21st (New Year and other religious days).
For recommendation ,I will be happy to offer you the services of my company - "Israel My Way - Customized Tours" (IMW), a local tour operator that specializes in planning and operating unique customzied tours in this country. Visit www.israelmyway.co.il.
You may contact me for further details - yoav@israelmyway.co.il
enjoy your visit!
Yoav Gal
Haifa, Israel