1) Student loans need to be paid off before you can serve, as you cannot have active debt while on a mission. I would see if someone in your ward (or someone they know) is hiring employees and use that money to pay off the loans. I also recommend making and sticking to a budget.
2) Support for service and paying for the mission itself will mainly come from your ward and stake if you can’t save enough on your own. The Church does not want finances to keep those who want to serve from doing so.
3) I would only do the one semester of school if you qualify for Pell Grant or scholarships or something not requiring more student loans. This is my advice though because my husband STILL is paying off college loans years after graduating and it is a right hassle.
4) You won’t be able to even start your papers until you’ve been a member for at least a year, and your availability date will have to start on or after your 19th birthday. So there’s time for the financial preparation.
5) Papers required to be completed (which you can get the Church to help with as needed):
Physical - updated medical records, a physical, certain vaccines, stuff like that. The form for the doc to fill out is provided.
Dental - dental cleaning, thorough examination for wisdom teeth and orthodontic needs, etc. Form for the doc is provided.
Psychiatric - if you have any history of mental illness, you’ll be required to do a psych eval. Mine was covered by the Church through LDS services.
6) After completing your papers you will have 2 interviews: one with your bishop, one with your stake president. Worthiness interviews are required before your papers can be sent off.