Most men have a morning wank to empty their balls. Get over it. My husband does it every day
I wish people would stop taking their own very limited experience and using it to massively over-generalise about the entire population.
OP, there's a lot going on in your posts and I think you need to take some time to separate out all the potential issues and work through them. Think through which ones are causing you the most upset and how you and your OH might work together to resolve them.
Masturbating is a contentious issue. Fact is most people, male and female, do it to some extent. For some, it is an extremely personal act that should be kept private, even from your intimate partner. For others, it's as trivial as brushing your teeth. You have to decide what it is that is upsetting you.
You mention the lack of sex and it seems you may feel neglected and second-best to his right hand. It's completely reasonable for you to feel neglected if that is the case and it may not be just the purely physical side of sex you're missing but the connection and intimacy with your partner that goes with it.
Porn is another contentious issue. Personally, I find it highly objectionable and have various concerns about its effect. One is the skewed view of sex that it potentially gives viewers and that ties in with your comment about him wanting to reenact with you things he's seen in porn. That tendency has the potential to be extremely damaging to your self-esteem and your relationship. Porn is predominantly male-centric (often misogynistic) and likes to push taboos and boundaries. You should never agree to doing anything that you don't want to do and don't feel you have to justify yourself either.
Final observation from me, and others have covered this, is the sharing of domestic responsibilities. If you are a SAHP and your partner works full-time, it is reasonable that you do a larger share of the domestic work. It is not fair or reasonable for you to be doing all of it. A household with 3 children and a baby isn't a 9-5 job. You will no doubt be hard at it from early in the morning and throughout the day so by the time he comes in from work you have both put in the same hours. If he thinks he can come in and switch off whilst you continue on with the housework and looking after the kids till bedtime he is taking the piss.
Overall, it doesn't sound like you have anything close to a good relationship. Lack of intimacy. Lack of support with the children. Pressure to do things you don't like in the bedroom. You deserve more than being a skivvy and occasional spunk-bucket. Whether it can be fixed depends on you and OH and it starts with open and honest communication. Gather your thoughts and speak to him.