Your Ideas for saving are good BUT you would need a car,and Rental car places only rent to people over 21 then they charge extra till you are 25.
So,staying onsite seems like a better option as there is Disney Transportation to everything. And to get from the airport to disney, you can take the Links Buses for under $2.00
http://www.golynx.com/fares/body_fares.htm
The All Stars Sports,Music,Movies rates are $109. to $49. with a code. With 5 people you will need 2 rooms. You can find at
http://www.mousesavers.com/disneyresorts.html#anyone
You don't say how many days you will be at WDW but for
now you can start deciding what are the things that are "must do's" and "must see's." and decide the length of your trip.
Then decide on the tickets you will need here.
http://www.mousesavers.com/tickets.html
To keep an EYE on All the discounts for on-site and off-site resorts check here often and sign up for the MouseSavers.com newsletter to get all the best news.
http://www.mousesavers.com/wdw.html
For Air fares sign up at all the Airline Web sites that fly out of your airport that fly to Orlando or MCO in airline speak. Then Check Expedia,Travelocity for airline deals. Also check out the Transporation Board air,car deals.
http://www.disboards.com/
Start a WDW change jar to save for your trip.[there are many tips here on this board!!]
Also you can decide where you will want to eat and start making plans to make your food budget and check the Priority Seatings Calculator to know when you can make PS's some are as far out as 730 Days.
http://www.wdwinfo.com/wdwinfo/dining/pscalc/dispscalc.html
Also to help decide where to eat you can find menu's at Deb's wdw site,this works 2 ways to see where to eat what,and how much it costs, to finalize the food budget.
http://www.wdwig.com/menu/menus.htm
To keep all this info in one place,here is a computer Disney Vacation Planner. It will print each day on a seperate sheet. Also check the pull down menu'sat the top for loads of info!!
http://www.intercot.com/planner/default.asp
Well,this should get you start on a thousand more Questions!! So,don't be shy! Ask away!! The kind members here will share what they know! So,check back often!!