1. MX 13 and 12 there is a range, no sub-grade. MX 11 there is 11 and 11A (AD & SAD)
2. When you receive your appointment letter, you will see your gross monthly salary and the breakdown, and the range of your current grade. You will be able to gauge how far you are from your ceiling within your current grade.
3. Yes. If you really get stuck for that long, you should consider alternate career choices or look for another position in another agency/ministry.
4. Years of service and performance are taken into consideration. Your education qualifications are also taken into consideration, so be sure to update your HRP profile.
5. Across ministries, titles may be the same but the seniority and grade may be different. Don't need to care too much about your title, care more about your grade and CEP.
7. I am assuming you are talking about grades in agencies like
DSTA or HTX where they run on the E1 to E8 rank system. I don't have too much information, but I think E3 is the equivalent of a SAD/DD if I remember correctly.
Don't need to think too much for now, learn as much as you can and do a good job, progression should come with good performance. Hope this helps.