How do you know the right therapy w/o a DX

[cetta5]

My 24 mth old has like 5 words/sounds (ugh-oh, WOW, Row row your.(won't say boat)..Shh.....grunts bye bye and will roar for a lion or SSSS for a snake.)  Most of time he sounds nasal and makes noises like his mouth isn't moving.  when he finds a toy he is looking for he occassionally will say There-it-is (slurred).  NO mama or dada or even yes.  He will nod  and grunt for "NO"

My question is, i have been repeating and repeating words(with pictures and actual objects) to him like ball, cat, boat, flower, shoes, apple etc.. Nothing.  He will point to those pictures in the book and look to me to repeat but nothing.

His receptive is weak.  He lays down when he sees his pamper, understands "get your shoes on" because he will sit on the step and give me his foot- same with dressing (put his leg in his shorts and head in shirt), go to pool- he will take my hand to the gate, same with swing or go in the car.  Very motivated by what he likes but can't communicate it.  He will take my hand and lead me to what he wants or reach to be picked up and grab what he wants from the counter (sippy cup, cookie, snacks etc..).  

He is social, points to things of interest to him, responds to his name v.good, not a picky eater, excellent motor skills, will throw ball back and forth, scribble on paper, eat with fork and spoon, waves bye bye alot but grunts it, will imitate his brothers and sister, has played with toy phone and pretended that a toy airplane will fly.  Loves, loves the pool and my best sleeper.

I have a speech therapist and a special ed teacher coming this week to start early intervention therapy.  I have 2 questions:
1.  what is the best TYPE of therapy when you don't know have dx?  What if he is apraxic or autistic and we try for months and no improvement.  what is the safest, most effective method to get the best results if he presents this way.  i see play therapy, structured therapy, ABA, etc...  I don't know -should i go to a neurolgist before we start therapy?
2.  Is there a point if a child doesn't approve they diagnose autism for lack of anything else?