Speech Delay and Starting School + Future of a Speech Delayed Child

Hi to all,
 
My son is 2.5 years old and has an expressive speech delay. We are in the process of getting him evaluated and have not yet heard back. We did an evaluation when he was younger and the doctors said they cannot diagnose due to ambiguity in his case.
 
More about him:
He only started saying words at 23 months old. However, he does understand everything very well, and in two languages. He says many words, some correctly and most incorrectly (wrong consonants, missing syllables, difficult and wrong articulation). He also attempts at telling us things / events that happen, in sentences but all we hear is blabbering, sort of like singing blabber. He has some mild sensory issues (pruney hands from water, refuses to eat fruits and vegetables, refuses to take baths), and is a bit more difficult than other kids (wants to do things on his own terms). Other than that, he does not present other obvious symptoms of ASD. He is generally very joyful and loves to be around other kids. We do not know if he has ASD or is it simply a speech delay / disorder.
 
We don't know much about ASD and don't have friends or family who are on the spectrum, so any replies and advice would be very helpful and appreciated.
 
We are concerned about a few things:
 
-When he will be of age to start school (around 5 yrs) will he be able to go to school and be at the same speech level as the other kids? If not, is it recommended he goes to school with the other kids? Or will he be placed in a special class? How does that work?
 
-Is it possible that his speech will not improve to the point at which he will grow into an adult who is unable to speak? (Considering he does say some words right now, is it possible he will not progress at all?)
 
-If he does become a non-verbal adult, what kind of life would/could he have? (Will he be able to write? Will he be able to work?)
-Is it typical that doctors are unable to diagnose a child at this age? Any parents with a similar situation, please let me know.
Thank you very much in advance.