I was on leave, from overseas, back to the states recently and hooked up with a girl who i had only briefly met a few years earlier. Hung out a few times as a group, had a date and hooked up, left for another state and got together again when i got back (she came to pick me up).
We had a strong and instant connection and both know that we would totally be dating if the geographical differences were not there.
After returning overseas I gave her a call that was fun and she messages me quite frequently. I got an app that lets us text for free, as well as SPAM. She wants to set up certain times for using SPAM video.

I understand that we will never be "exclusive" while I am over here. I do have many questions regarding the situation.
1. IF the topic of: what are we?, should we try a LDR?, or questions about dating in general come up, what would be an appropriate response?
2. Limits on calling, texting, and SPAM video.
3. How to keep her sexually interested (as I am not there to physically escalate).

I'm basically trying to keep a good thing going until I can get back and be there in person.

I think I have number 2 down but my main concern was with number 1. IF she ever brings up the topic of "what are we", or otherwise trying to define the situation, what is a good move to not come off as needy/lonely but also not as the opposite (someone who does not care at all)?

seems like you are doing fine. i would think that yall are really good FWB at the moment. And if question number 1 comes up, i dont think it is something to directly answer immediately asked. If the topic comes up i would say something like "lets discuss this over the next couple days and come to a conclusion at the end of the week." Then over the course of the week, discuss all the pros and cons, and concerns with each other bout it.

Going well so far, texting a few messages back and forth every 2-3 days, and using SPAM maybe once a week or less. I said we should SPAM at a certain time and day and got this answer.
"I won't be able to do Sun because (insert sister name) is not leaving until Monday. I mean we can SPAM but not about sex stuff".
Now I'm trying to decide should I SPAM anyway at that time and build rapport with sis or friend (whatever she is), or choose another time and get things more hot and heavy.
Any pointers on talking dirty through SPAM and it leading to watching each other "play"?

I would offer to SPAM as long as it didnt interfere with her time with her sister, and tell her absolutely understand the no sex talk while people are around. If she agrees have a short friendly chat and then next time you two SPAM, she might be app to do a little more than usual