it could be the way you're talking to him.
I think it's extra hard for people who have been in high level jobs where they're managing others because you get set in a way of communicating that's very adult and straight down the line. If you mean no, you say no. Etc.
With kids it can help to head off tantrums so often, if you say what you were going to say but in a different way. Like with the garden thing perhaps when he said he wanted to go out, it might have headed him off at the pass if you said "Oh, YES, ds, WHAT a FANTASTIC idea, lets go in the garden, as soon as it stops raining....you look out, is it raining? It is? Oh, look at the raindrops falling down the window...shall we blow some bubbles while we wait?"
etc etc
I know that sounds lame but I just mean it's about talking to them in a different way.
I used this sort of approach with my ds who is very strong willed, and it worked well.
of course nothing works all the time and children WILL have tantrums. I think you're spot on that ignoring it works best.
I tihnk it's good to give yourself permission to have some minutes here and there; like having your DH hug you, that's not something wrong or something you should allow him to try to bust up. It's ok to be stern with him about stuff like that IMO. Don't let him bully you too much.
Have you read 'toddler taming' by Christopher Green? It's really good for making you realise that many children are this insanely hard at some point in their early years and he's got a humourous approach which helps.
BTW I do agree that working FT is a good option, not saying that in order to be a 'good' mother you must stay home and suffer - just that if you want to be home for his early years, other strategies may help you get through