1. duften and riechen
duften is only used for scents that smell good (the meaning of this word actually has a strong emphasis on "smelling VERY GOOD"). flowers, fragrances, parfume, good meals etc. The cannotation is positive.
riechen just means "smelling". it's used to describe all kinds of scents, good, bad or weired smelling ones. riechen itself is neutral. It's like saying "it smells". Now what? How does it smell? Good, bad, funny. RIECHEN just describes that you've noticed a certain smell. You additionally need an adjective to make it clear.
2. satt and voll
basically means the same.
SATT is a little - just a little - bit more formal.
3. abspuelen and waschen
abspülenl iteral= to swill
abspülen colloquial = washing the dishes.
waschen= to wash (cloth, your car, etc).
BTW: washing the dishes = Geschirr spülen
4. fertig and bereit
1st means "finished" second "ready"
5. leihen and ausleihen
lend and borrow
6. fern and weit
far and wide
7. spaet and verspaetet
late (as in "hurry up, it's late") and the second (delayed and being late.
8. sitzen and sich hinsetzen
sitting and to sit down