"Wipe Everything"? What should I wipe?

First of all, Merry Christmas and welcome to the community.

As for any "wipe everything" statement:

Format System, Data. Under the advanced menu -> format
Under the Flash Zip menu, select to wipe cache and dalvik-cache.

Generally any zip flash is going to re-format system if it needs to, but it doesn't hurt to be sure that it is done.

1.04 should be ok for most roms unless the rom creator mentions you need a specific hboot. I run 1.40 and I've never really changed it and everything i've flashed works ok. You may flash any sprint rom you like, whether or not your APN settings or MMS will work is another question. Currently anything that doesn't have sense means your MMS will not function correctly if at all. Which is why any "sense-less" rom here keeps the sense framework around for the mms app itself.