two firsts! introducing a kitten to a cat and... joining a forum

i hope someone can advise us on our next move.

we have a two year old male (neutered) cat who is very friendly and quite passive but has had to frequently work hard to defend his territory against tom cats. this is not always completely successful as we get spraying just inside the cat flap However our vet says he is physically very capable/strong.
on sunday our 13 week old female kitten arrived. She is confident and feisty and seems to have settled well. we have been following forum and vet advice and have seperated them, initially swapping scent through cloths then putting our kitten in a box and allowing our older cat to explore the room. This has been going really well with our older cat sniffing and weeing in he litter tray and today they had breakfast side by side with kitten in basket and older cat next to her. Following this i let the kitten into various other rooms/places enjoyed by our older cat and then encouraged our older cat to follow her scent.
tonight we again used the basket to give them some more time in each others company. our older cat was not aggressive despite the kitten growling at him. However he eventually pounced on her (safe in basket) after i had stroked him as a reward for not doing this!
We put the kitten in another room and ensured she was ok. our older cat hid behind the sofa and then went and pooed in her litter tray.
we are commited to giving them both time, encouragement and attention, when they are together and also seperately and we know that this is a slow process.
My question is: how will it work if the kitten continues to growl thereby possibly agitating the older cat?
if this continues should we let the kitten out of the basket since this is a more realistic approach?
thank you