im going to sample drums for 3 hours on sunday, after that ill only use my own samples for everything. for a bit and see what that might come to. if it doesnt work ill try something else but im real excited about this.
Go for it man - I always find I get a few really useful samples I've not intended going looking for when I do that so keep your ears open.
To answer your other question it depends really. All my basses and mids I make myself on a synth (usually analogue) but then quite often end up re-sampling and fucking with the sound some more so I guess you could say that even those are samples
Atmospherics and whatever I just get from wherever - sample CDs, sampling other things, synths, processing - and usually end up combining all sources.
I guess my point is never shut yourself off from a source of sounds just because you don't think it is 'doing it properly' - you are only doing it properly when you make a tune you can get into and makes you want to dance. How you get there isn't important, it is the result that matters not the method.
IMO there are a lot of really well produced tunes out there where you can hear the hours that have gone into crafting them but at the expense of the vibe of the tune. Never let production get in the way of the vibe.