If you really have 8 park days, consider an annual pass--that's about the break even point---if you think you might come back within 12 months, could be a great deal.
I don't know if there is an 8-day parkhopper, only 7-day parkhopper plus. Yes, you can go to any or all of the parks for 7 days with the 7-day PH+. The PH is a little cheaper than the length of stay (Ultimate Parkhopper), and the plusses and any unused days never expire. Of course, with the Parkhopper, you have to use your plusses to go to a water park (it might be warm enough, it's hit or miss that time of year) or to Pleasure Island, and Disney Quest isn't an option.
If your 8 days includes arrival and/or departure days (or even if it doesn't), I'd even consider getting a 6-day PH+ and planning on park off-days. With a little planning, you can do quite a bit on the park off-days.