New here and very first post! So please be nice!

Just wanted some advice, and perhaps reassurance that I am moving along the correct lines here! I have always had cats and have successfully integrated two of similar ages and characters, but an older cat and kitten is a new realm and so I am trying to be a sponge to make sure I take on as much good advice as possible!
We took in a 6 month old rescue kitten just under 3 weeks ago, but also have a 10 year old female cat who has been with us over two years. She moved with us to our new house, and so for the last 16 months, it has been me, her, and my partner in 'our' house. Our female has long been neutered and little man was done shortly after arriving.
She tends to be a house dweller, who likes to have a stroll in the garden, and to sunbathe in summer, but other than that, likes her home comforts. I would say she is a shy but friendly character. although when she arrived with us she was quite anxious for some time. It has taken us along time to gain her trust and her to enjoy a fuss. She still doesn't sit on laps, but will stand near you or happily be picked up for a stroke, but once she has had enough, she likes to get tucked up in her fave spots. She is pretty chilled out now she knows us, and definitely is not a dominant character.
He is obviously full of energy as a kitten, but there is absolutely no malice, he is a gentle and kind kitten, who seems quite naive still, which I thought would be better as he will then learn to accept her boundaries a bit easier whilst learning from her. He is a cuddly, friendly and confident little critter, but he isn't stupid and he knows where (most) the boundaries lay with behaviour, although needs the odd positive reinforcement.
Clearly adding a kitten to the mix we know it is going to take time for her to adjust (and that can be up to months!) and we are taking it very slowly. I am also conscious though that the longer it takes, the less likely it is she is to accept him!
To explain, for the first week he had his own 'safe' room, and she had the run of the rest of the house still, making sure she had access to the room with her favourite spots. Then we gradually allowed her to smell his area, rubbed them with towels, exchanged scents etc, allowed them to smell and see each other through the door (doors with glass came in handy!), before allowing her into the room with him in his carrier. After doing this for a few more days (although she couldn't really be bothered to inspect), we have allowed him into the rest of the house with supervision. At night and when we are out, he is kept in the 'safe room'.
To be fair, they don't fight or show any major signs of aggression and he is completely oblivious to it anyway. He occasionally goes to pounce playfully which she clearly doesn't like as an older lady, but she just hisses and so far there have been no major run ins... fingers crossed! He is slowly learning not to pounce or chase, but as a kitten he has lapses, and so until we are sure there will be no run ins, they will be kept supervised. We try to wear him out with plenty of playtime too and I hope that once he is allowed outside, he will burn up his own energy!
Our older cat always gets some downtime in the evening with us, and I always make sure to give her fuss. Little man also gets fuss but I try to make sure it isn't done too much in front of her as to not confuse her place in the hierarchy. She has done the usual of hissing at us because of the new smells and routine, but when he is on 'downtime' she happily has a cuddle like usual.
I have also bought the feliway plug in, which has been in about 24 hours, and also the pheromone spray, which she LOVES. I have sprayed it in areas to try and encourage her back into the rest of the house, which worked last night, as she slept in the bedroom for the first time in 3 weeks and he left her be. I want to continue encouraging shared space, rather than split territories, but don't want to force it. She isn't hiding away either, she tends to stay in the same room as she was in although she will move to a different 'area' at times, and she has a defined 'safe spot' at the minute, so I try to make sure he doesn't invade this too much. I don't however want her to end up clinging to that area forever more, but she is slowly becoming more mobile around the house again at times, like the other night.
I have a spray bottle to hand to reprimand bad behaviour in little man, and also treats for both of them when they are relaxed and peaceful. They get fed in the same room together, but apart, enough to see and smell each other. I am trying to get them associating each other with nice things. They eat peacefully within proximity.
To note, there are two feeding areas and two litter trays. His are within his 'safe' area and hers remain in the same place. I have to sometimes remind him not to steal, but gradually he is getting the hint about 'his and hers' bowls. She just tends to sit and watch him if she does catch him stealing.
There have been some very peaceful moments where by they have sat happily near each other with no issues, and have slept within a few feet of each other. Not best friends, but neutral/mutual ground.
My only issue is that she continues to hiss at him either when he walks near, or when he first enters the room. There are moments of no hissing, usually once he is sat still, or has been in the room a while. Should he move again she then will have a short hiss again. She doesn't outwardly strike out at him, and he ignores her and carries on, or rolls over in a submissive way near her. It seems more of a threat that she wont (and so far) hasn't really acted on rather than a 'I am ready to attack' noise.
Occasionally when he is in 'play' mode he continues to stand near, almost touching her & sniffing, and she just continues to hiss (in which case I distract him away from the situation). She will tend to hold her ground until he wanders off, or she'll then move elsewhere. I tend to back her up a bit to reassure her by removing him when I know she needs a break, but other than that, I am trying to let them find their ground with each other a little, as long as fur isn't flying, and they are both relaxed. She definitely isn't stressed or anxious as such because once the moment is over she goes back about her business or will very quickly settle down to rest or sleep.
Am I right by allowing them to sort out their own hierarchy a little whilst supervising, because I assume that is what she is doing? Do I need to backtrack on any of the steps? And is there anything else I can be doing to help things along? I am not concerned that there is any major aggression or issues cropping up right now, but am I heading the right way, and how long will this take?! As I write this one is asleep on the couch, and one on the chair a few feet away. So again, neutral sharing of territory.
Ideally, and long term I want them to share the full house, rather than split areas, but I know this will take time!
Thanks in advance!
