Tbh at 8 months in, I'm not surprised he doesn't think of you as a family unit yet. He can care a lot about you both, but he probably thinks it's too early to be seeing it that way. It was a couple of years before I was at that stage with my partner.
Based on this situation alone, I feel you're being overdramtic. But... the takeaway at Christmas thing would annoy me. If he decided against the takeaway in favour of the leftovers, it should have been him putting some food together, not you. I'd have been tempted to get myself a takeaway and let him crack on.
Then this situation with the mini break. You can't afford it. There's no point him going on at you about it, because you can't magic the funds out of nowhere. He either leaves it and waits until you are in a better position, or he can pay for you both, with no expectations of you paying him back.
It seems like you might not be compatible tbh. Sometimes when there is a financial disparity in a relationship, it can cause resentment. You think he should be more generous with his money, especially when he knows you have much less, and you resent his perceived tightness.
He'll resent that you might automatically assume he should put his hand in his pocket because he is better off (even if you're not, this is what he's perceiving), and that you aren't able to do things together that he would like to do (like the mini break), unless he pays for it.
It may be worth having this out with him if you think the relationship is worth hanging on to, because this situation seems exhausting. Although it is fantastic that you and your DS get on with his family so well.
Otherwise, you might want to reconsider it altogether and find someone who isn't quite so "tight".