To fix the "It doesn't let me upload" issue,
take a look here (BSS issues)Regarding the part, if you can use stuff from other maps, I'm not 100% sure, but I think the answer is mostly yes.
(Correct me if I'm wrong)
Background: Unless there is an indicator that the mapper made the background, you can simply assume it's from somewhere on the internet, most (if not all) maps ranked as of late to have the source linked (either in the maps description of somewhere in the discussion tab)
Timing as in uninherit (red) timing points usually aren't a problem, especially if you use the same mp3 file it's encouraged to use the same timing (bpm/offset).
If the timing of the map is
rather complex (taking
this map by
pishifat for the example), I'd suggest to credit the mapper for the timing.
For timing as in slider velocity changes, I would take caution and rather ask the mapper for consent, especially if you are going to copy and use it as is.
(Base) Slider velocity in itself is just a setting, no one can blame you for having the same setting as in any other map out there.