A general query regarding XP & Skill Levels. Currently on Level 18:
a) Does it improve my XP & skill by going back to earlier levels and killing the beasties?
b) If I play one of the download content levels do I keep and improve my skill levels or are these totally separate mini-games?
c) If I do play a download content level does the main game remain un-effected or changed?
A. The best way to xp get so is to do side quest and kill things that are close to your level. Same goes for side quest make sure there close to your level.
B. The dlc does give you Xp just like the main game
C. Depends on the game mode you in nvhm in you case. If you do the dlc in nvhm you may or may not out level the main story depends on how many side quest you do. I have a character that is doing all side quest and main quest for every dlc and main story who’s level 45 in nvhm.
(Flying: throwing yourself at the ground and missing)
XP scales inversely with the difference between your level and the map level. Since most maps in normal mode don’t change their level, you’ll get diminishing amounts of XP per kill. So going back to Southern Shelf Bay you will find it much easier as a level 18 to kill the bandits and bullymongs, but the amount of XP you get will be very much lower. The main reason for going back would be to practice your aim, or different combat tactics.
To add to the answer you already got, you keep all your level and skill points: they’re tied to your character, not the individual game, DLCs, or headhunter packs.
In NVHM, the levels of the maps and missions are pretty much fixed. Some main story missions will cause a rescaling of specific maps (e.g. Sanctuary increases in level a couple of times.) One thing to note in addition to the previous answer: some of the expansion content has a minimum level, so if you start it too soon you may be under-levelled. A second thing is that travelling to the starting location for any of the expansion content sets the initial level (either to its minimum or your current level, up to the maximum level for NVHM.) So if you wanted to get DLC1 mission rewards at max level (30 in this case), you do not want to go there until you’ve completed the main story.
You’ll find similar questions in the main Discussion and Discussion (Spoilers) sections for the game, so you might want to poke around there too.
That’s not precisely accurate. You’ll set the map levels by your first visit to each map, but the quests will be at whatever level you are when you accept them, up to the DLC max level.
For example, on Maya I did DLC1 during NVHM, with a first visit around level 17, then a second batch of quests around 24 (including Wurmwater and I believe Washburne Refinery as well), then finished the last part at 31-32. My Sandhawk and Pimpernel are both level 30. You do need to take care not to accept those quests until 30, obviously.