Mel I dont have a lot of time to reply right now, but I just want to say that WRT the multiple issues that are going on with Jacob-
I feel like I have been through something that sounds SO similar over the last few months with Aidyn.

The hitting/throwing & crying tantrums were driving DP and I bananas, and I honestly was doubting my mothering skills, wondering how I could have raised such a violent child! But then lo and behold in the past 1-2 months the hitting has drastically reduced - very nearly stopped completely, and the throwing has been cut down by over 50% too... But boy it took a while... I think he was in that stage for about 4-6 months.. and it wasnt pleasant. I would say to just continue with exactly what you are doing - telling him that hitting is not acceptable and he must be gentle, etc, etc. I really think it will get through... unfortunately it may take another couple of months (if going by Aidyns age/stages is any indicator)

We also went through some food dramas, though not that extreme... and TBH I just let him eat what he wanted, as long as it wasnt very junk-like or too sweet etc.
We have found that he much prefers eating at the same time as we do, and prefers even more to eat off our plates rather than his own. Its not a habit I want him to get into, however if he hasnt eaten much that day, I certainly wont stop him from doing it iykwim.
I also try to regularly make up batches of wholemeal fruit & bran mini-muffins, or vegie muffins which he sometimes will eat when all else fails.
Another thing I do is if he really doesnt want to eat his dinner, I then give him a range of semi healthy (and easy) alternatives - such as fruit, or pieces of cheese... and I know its not ideal, but I suppose its better than nothing.

I guess it could also be quite possible that the dislike of food could be related to his molars coming through too maybe?
I noticed about 2 weeks ago that Aidyns 2year molars were fully broken through, and I wonder if that had something to do with his recent improvement in behaviour & eating.

Oh and another thing... Aidyn also eats well, and behaves perfectly at daycare, and whenever anyone else is looking after him... and always has! So maybe it has something to do with them feeling so comfortable in the home environment and so used to their parents that they feel more able to 'let go' and tantrum, as opposed to when they are with someone other than mum or dad, or in a place other than home. And boredom may also come into it as well as a factor for why they get frustrated and cranky...

Also being sick can effect them in more ways then we can pinpoint I think... After Aidyn has been sick, his sleeping routines usually go totally feral for about 2 weeks afterwards.

Anyway, sorry I have just realised how disjointed this all is 8-[ I hope in all of that I have been able to offer some sort of advice or reassurance that may be useful to you.
After feeling like I have experienced similar stages with Aidyn these past 6 months I really just want to tell you that I'm so positive that Jacob will grow out of it fairly soon.
Huge *hugs* and please email or PM me if you ever need to chat, or just vent.