DIY Wardrobe insert shelves

[DexterOz]

I have wardrobe with no shelves or partition, so i want to build standalone insert shelves that sits between

the current partition. I have tried to measure and put down on paper roughly. 

Question : a)  Is that the correct way to measure or do i need to leave more margins on side 

b) Is melamine particle board good for wardrobe 

c) Do Bunnings cuts board to size or i can cut using reciprocating saw 

d) What kind of screws to use with melamine 

Any additional tips for first timer

Thanks in anticipation 

[DexterOz]

Noyade no there is no back cover