that's something which you'll find in the manual.. and of course you can modify OSC 1

Of course you can, but you should definitelly read the manual to see how. Nord Lead 3 is a very powerfull machine but you gotta know how to use it. Other than that, download bass patches for NL3 from Clavia website to give you a good starting point for your own bass sounds.

I have a book from wizoo called "Analog Synthesis" which I used to get me started to help me understand synthesis. Once you understand the basic elements of how a analog synth works it isn't that hard to program. I don't need it anymore and i can sell it to you if you want. It helped me a lot in the beginning..when I got my first synth..the Waldorf Q KB. PM if your interested.

yes you will probably want to look into subtractive synthesis to get a good idea of how the nord lead works. basically you generate a flat tone on 1 or 2 oscillators (just like those frequency generators in a level physics classes). then you shave off the frequencies you dont want on the filter. hence subtractive.

dunno about the lead 3 but the 24db filter on the lead 2x didnt sound right. if you turned up the resonance it would sound unbelievably thin. when i messed around on a lead 2x i had a few problems trying to make fat, warm basses on it. but theres alot of experienced people out there that swear it can be done so id take their word for it and start twiddling. thats what makes nord leads fun! you sit down. and you twiddle for hours.

I don't know about getting nice phat warm basses out of a Nord(1,2, and EX that is)...well don't get me wrong I have got some nice basses mind you but they are better off used to layer with something with more bottom end. The best thing about teh Nord is that it can just rip right through a mix.