Newly diagnosed son and scared parent

My 3 year old son has just been diagnosed with ASD. We completed a questionnaire with the paediatrician, they confirmed diagnosis and gave us some leaflets to read at home. Now I feel like I have been thrown into this world that I have little understanding about and worried about my sons future. I wasn’t able to ask the Dr any questions because they were running behind. I’m hoping to get some help/support from other people on here. 

My son has an expressive and receptive language delay. He is currently non verbal and will pull you to what he wants or bring it to you (the remote control if he wants the tv on ect) he can say and read numbers and letters and enjoys nursery rhymes. It can be difficult to get his attention and he can lash out if he doesnt want to do something (pinch and slap) he likes to engage with children but as his communication is limited he finds it difficult he also doesn’t understand the concept of sharing and his play skills are delayed. He doesn’t have any routine/food/sleep issues. 

for all the parents and carers out there with children with ASD does it get better? How will I know if he is going to be high or low functioning? He is on the waiting list for speech therapy, is there anything I can do to help him progress? 

I know everyone with ASD is different. It would just be good to hear some of your experiences and share any advice with me. 

I have spent the last couple of days crying and worrying my son will never develop. I have decided it’s pointless crying and being upset and I’m putting all my efforts into helping him. Any advice on where to go next would be really helpful!