hi there
poor you - the early days are really haard work and they do feed and feed, it's part of stimulating your milk production, aswell as using you as a filling station. you will have enough, esp. if you're demand feeding. supply=demand: he feeds you supply.
you sound as though you're doing really well and you are right to feed on demand as this too helps to stimulate supply and also makes sure baby gets exactly what he needs and when. try to think of your boobs as the kitchen and then think how often you go there to get a meal/biscuit/cup of tea/ glass of water etc throughout the day. he has to get all that from you.
in terms of how long they feed for... well because of above, it does vary and as long as he feeds for as long or short as he needs to he is getting enough. he doesn;t need to feeed for a certain length of time to reach the hindmilk - that's not how boobs work - which is reassuring as some babies (mine included) would never get to it.
do you mean he's feeding every 10 minutes or that he has a break for 10 minutes before going to the other side and then he settles for a bit? if he's just having a break change his nappy or whatever then put him back on the other side when he stirs so he can have his pudding, (and start the next feed on the same boob you finish on).
in the early days, and 9 days is still very early days, he might seem to be feeding constanly and it is hard going. iirc they have a growth spurt around 10 days or so and will have a feeding frenzy. they do cluster feed at times and again this helps your supply, and fills him up to sleep for a bit longer; he just hasn't realised yet that cluster feeding in the middle of the night is a killer!!
you're doing really well and you will get there. it does get easier - honestly it does (that's not just a cliche). it doesn't stay like this forever. wrt ff, don't beat yourself up about any decision you feel you have to make, you have to be able to get through the day, but you might find it doesn't make that much difference to the feeding/sleeping pattern. as you already said, he took 3 oz and still woke up half and hour later to feed for a further 2 hours.
there's nothing really i can say that will make the reality of the tiredness any easier but i do sympathise, and it does get easier, this stage does pass.
hth