P scales are a way of assessing children with SEN that are not accessing the curriculum
SEN children in a mainstream school would probably be above P levels but you may have some with specific needs may have very spikey profiles and really struggle in certain areas so may be functioning quite low
You really need to find out quite quickly where they are at ability wise -can they write a simple sentence independently, what is their reading age etc.
Class layout is personal choice -I like a u shape wth a small group in the middle -means I can see everyone, they can see me and it's easy for me to move around and work with target children
Behaviour wise, short simple instructions -you really need to break things down and not give multi step instructions.
They will need time to process what you say, don't rush them.
Compassion and understanding goes a lot further than detentions and other sanctions
'I'm happy you want to share -hand up thank you' will work better than 'don't shout out'
-depending on what their aural processing is like, they may only retain 'shout out' and do it more
Tell them the desired behaviour, and positive praise when they do the right thing
How much support will you have in class?