Its ok, I understand how alone you are feeling with it all. It can be terribly isolating going through all this stuff. We've all been there at some point and we are all here to help each other. 
Based on your list he does sound a lot like my ds, excluding the physical and violent stuff as my ds tends to implode rather than explode iyswim.
I'm no expert and only have my own experiences with ds to go on, but imho there is definitely enough there to warrant further investigation. I would think your GP should refer you to a paediatrician based on the things you list.
If you do go to your GP, try to get referred to a Developmental Paediatrician rather than the Community Paed. That said, not many GPs will refer straight to Dev Paed as there aren't enough of them to go around. We were lucky as our Comm Paed works with the local multi-dip ASD assessment team as well.
The school are able to refer him as well, but in our case the school steadfastly refused to see there was a problem and we had to do all the legwork so-to-speak.
Its well worth pushing now as if he is likely to find transition to secondary particularly tough and it would be good if you could get some support in place for him beforehand.
While you are waiting to be seen by the Paediatrician, you can be pushing the school to give him extra support with his social/communication issues. He doesn't need a diagnosis to get help and support. As others on here will tell you, you are the expert on 'your child', you know best where he is concerned, so don't let them fob you off.
This page from the government's website gives some basic information on the Special Educational Needs process and you can download their 'Guide for Parents and Carers here.
In the first instance he should at least be placed on School Action and given an IEP (Individual Education Plan) which will set out the areas he needs help with, what the school is going to do to to help and how they are going to do it and will also set targets for him in each area. They are usually drawn up by the SENCO and in our case we are allowed to attend the review meetings and they are also attended by his teacher and in future will include the ASD inclusion team and the Ed Psych as well. If he doesn't make enough progress or meet his targets on School Action over a few IEPs they can progress him onto School Action Plus, which is when outside professionals and agencies become involved in the process.
Hope that helps a bit. It all seems really big and scary when you first start looking into it, but you do start to get your head around it. We have only been going through the process since November 2009 ourselves.
Oh - and don't stop asking questions and coming on here for help and support. This is a very supportive place, the people are lovely and you will learn far more here than you will ever learn from books, websites or the so-called professionals.