Inputs requested on school procedures in Sydney

Hi!
My husband and I are planning to relocate to Sydney in the next 2-3 months . We have two sons - one is 11yrs old who has developmental delays and passed 4th grade and now he needs to get into 5thgrade , I am worried about his school, can somebody help me to understand what is the general procedure to get into schools ,and which will be the best schools for children with mild difficulties. Till now he used to go to normal school setup but i was fully guiding from home . My second one is 4yrs old he has is well adept in writing and reading skills which are age-appropriate. Appreciate if I can have the following inputs:

1. What is the procedure for admission to schools in Sydney mid-way through the year? (we might be landing in Sydney in the June- August timeframe)
2. Can anyone guide us on whether there will be any special procedures for admission for children with mild learning difficulties?
3. Any idea of the financial requirements to support a child with mild learning difficulties (understand that the cost for a child in a public school is A$ 4500 per annum, are there any special fees levied for supporting children with learning difficulties)?
4. Any inputs on supporting infrastructure availability (Occupational Therapists, Speech Therapists etc) will be highly appreciated - are they easily available, what will be the charges etc.

Sorry about the multiple questions, but we are terribly anxious and hence appreciate any inputs on the above.

With warm wishes,
Sandhya.