Vic, I'm so sorry this has happened to you. I can understand something of what you're going to as I lost my husband to cancer in August. I have two DSs aged 4 and 5. In my case, we knew his condition was terminal and lived with that knowledge for 18 months so had plenty of time to get used to the idea and prepare for his death (I won't say 'accept' because I will never accept that he had to die).
The best advice I can give is take one day at a time. You will be going through so many conflicting emotions that change from day to day, hour to hour even. Plus you not only have to deal with your own grief but your children's emotions as well. That is hard, very hard. I won't pretend otherwise. What I have done with mine is to take their lead. I believe that children instinctively know what they need. DS2 sleeps with me almost every night. He obviously needs the comfort and that is fine by me. DS1 sometimes joins us, sometimes prefers his own bed. Again, that is fine. If they want to talk about Daddy, we talk. We look at photos together. We look up at the stars every night, pick the brightest and say 'that is Daddy's star and he's looking down on us'.
A lot of the time, they just carry on like normal. That can be hard too, especially at the beginning. Your world has come tumbling down and you look at them and wonder how they can laugh and play but it's the best thing for them. Try to stick to their routine as much as they can as the familiarity will reassure them and be comforting. I found it incredibly hard to take over the bathtime/stories/bedtime part of the day as DH had always done that but they needed that continuity.
Your DS's anger is a perfectly normal reaction. My five year old is going through the same stage which is very upsetting as he's normal a sunny, happy little person and these rages are hard to handle. I just try to ignore them as much as possible, give him lots of hugs and reassurance and hope that the phase passes soon.
Above all, don't make too many demands on yourself. There is no 'should' and 'ought to' when you've lost your husband. Do things in your own time, when you're ready. Do try to eat, even if you don't feel like it, as you need to stay healthy but don't worry about anything else.
If you want any advice on practical stuff or just want a virtual shoulder to cry on, CAT me or keep posting on this thread and I'll keep checking.