Keep in mind that every college admissions office evaluates candidates differently. My response to your questions, therefore, is based on generalizations and are not necessarily true in every case.
"-How do I overcome the strict requirements that most universities have posted as their 'freshman admissions checklist?'"
You've already overcome some of these by giving years of service to the military. Military service trumps a list of extra curricular activities from the average freshman applicant.
"-Would it be advantagious to me to complete 2 years at a community college before attempting to apply at a major university? [I was told that a good GPA over 2 years at a CC would trump my poor transcripts/CHSPE problem.]"
It was for me. I was a student in a similar situation as yours: poor high school transcripts, no SAT scores, ect. When I completed my active duty obligation, I immediately went back to school, took a full course load consisting of rigorous courses. After two years at CC, I had a 4.0 GPA, was a member of the Honors program, and received a prestigious merit scholarship. I applied to some top universities and colleges and was accepted to each one. Admissions did not care about what kind of student I was in high school because it had been about 6 years since my senior year. They wanted to know who I was at the time I applied.
"-Will my MGIB cover student housing and other costs of being a full-time student?"
You're probably going to want to use the Post 9/11 GI Bill instead of the MGIB. It's more comprehensive, covers housing, and makes private colleges actually affordable. You can read up on it here:
Education Benefits - (U.S. Department of Veterans Affairs)
"-How can I use my status as a combat veteran, and the other military accreditations/medals to my advantage in a competative school's"
Write a compelling essay which shows the admissions office how your military service changed you as a person (that's what I did anyway). Other than that, there will be places on every application where you can list your various accomplishments. However, from one service member to another, let's be honest, unless one of your awards was awarded with Valor, it's not that big a deal. Seems like everyone gets Arcoms, AAMs, and even Bronze Stars nowadays.
"-Other than studying for the SAT, what else should I be doing to prepare in my downtime? (What little of it that I have.)"
You can study for the SATs now if you want but if you're taking the CC route, that won't be necessary until your apply for transfer. Honestly, no preparation might be the correct course of action other than mentally preparing yourself for the transition to civilian life. You can start thinking about what CC or state university you would like to apply to and research their admissions policies. You can look through course catalogs and think about what you'd like to study.
Hope this post helps you.