Hi and welcome! I have a 4.5 year old son wth ASD - I recognise many of the things that you describe from when he was 2. He wasn't dx until he was 3.3 though, and I think it's great that you've got such an early start with your DS. I also remember being overwhelmed by all the different approaches on offer - and feeling this tremendous sense of responsibility and pressure to choose the 'right' one. I thought I might write about what we've done so far - but apologies if it's long winded!
We started by concentrating on Floortime, which I learnt about by reading Stanley Greenspan's book, 'The Special Needs Child'. This helped his social interaction no end - he is now a very responsive child within the family, though less so 'out and about'. If you google floortime you'll find a website too (this may have already been mentioned).
I did tons and tons of singing and reading, not pressuring him to talk at all, but just leaving gaps here and there - and after a while he started to fill them in. It sounds as if your son responds to music, so this might be worth trying. A lot of the songs I did had signs attached (from Sing and Sign, Something Special and the Dave Benson-Philips Makaton nursery rhymes video). Although he's never signed much himself, it did improve his receptive language a great deal - having something to look at as well as listen to seemed to reinforce the word somehow. At this stage (2 -3.5) he was saying a few single words but they would come into his vocabulary and then just drop out again, so that he never had a 'working vocab' of more than 5 words at a time.
When he was 3.5 we introduced PECS (their course is really worth going on; would highly recommend it) and this is when he began to use functional language - again, only single words and limited to the things he really really wanted! At first his speech was always prompted (he'd give us the PEC card and we would say 'I want ......' and see if he'd fill it in. From about 4 he started using words to request things spontaneously and he now has a slowly growing vocabulary which he seems to be retaining - still only single words (with a few learnt phrases like 'timegohome?' ) and still only for stuff he really really wants - but it's a hell of a step forward from 'dickerdicker dicker', which is all he used to say at 2.
At this stage though he was still refusing to do any adult initiated activity (except singing and looking at books). Any attempt to teach him anything directly was completely rejected.
Since he was 4 we've been doing a home programme which is run by Growing Minds (review on Gess's website) and is based on ABA/VB. We've also started a biomed regime, supervised by Mike Ash of Nutrilink (again you can google; sorry, crap at links). These last 6 months have seen the biggest advances so far in that he can now sit at a table for up to 15 minutes, follow receptive instructions and is learning skills like imitation, matching, playing with toys appropriately and labeling objects and pictures. He has become far more responsive and affectionate, often seeking us out rather than being happy on his own. Although he's still very obviously autistic I feel very positive about his progress (although I still have black days from time to time).
Hope some of this LONG post is helpful. You'll get tons of support and advice on here - it saved my life when we were in the early stages of dx and I still regard the mums on here as my major source of info!