Next summer, after i graduate from ucsd i plan on taking a roadtrip around the US with my younger brother who will be 16 and a half and a junior in high school... I'm hoping it'll be one of those life memories, so im starting to plan it out now so that we'll be well prepared when the time comes (2 summers from now). Here's what I've figured out so far...

We live in San Diego, And we're going to driving through arizona and such to texas. In texas, we're going to check out a couple universities for my brother, and also hit up all the six flags (we're both into rollercoaster) which brings me to my first question... Is there some special deal with six flags in which if you have a season pass to one theme park you can go to any of the other ones? if so we could make it a theme road trip :)
from texas i wanna drive down to new orleans... when's mardi gras? last i checked it wasn't in the summer... but it would still be fun just to say that i've been there right?
from new orleans we'd drive thru those southern states and go down to orlando... spend a couple days at walt disney world.(gonna be expensive)
from orlando we're gonna go up the east coast, is there a beach highway? (like the 5 on the west coast)
hit up all those old ivy leagues... visit boston, DC, NYC Philly... from there we're gonna go to montreal to visit my aunts, and then where? yellowstone? and mount rushmore? is there anything else to do up in the northern states? wheres old faithful? then back down thru cali and finally back home...
i was hoping to do this trip in 3 weeks in my honda accord... is this wise?
we're planning on sleeping at least every other day in my car... and then showering when we could...

is there anywhere i can get free maps of landmarks and places i should see at least once in my life? am i missing anything? how much money should i allot for the entire trip for the two of us? What are some tips on how to save money? how many miles is it from coast to coast? and width? will the weather be too bad? are there any unforeseen things that i havent mentioned/thought about?

insight would be greatly appreciated :)

oh ya... when we sleep in our car... where should we sleep? where would it be safe?