Yes, should be "di-ya" instead of "di-a"

Yes, i think it is the most correct grammar

but to be honest, indonesia people rarely say "pensil-pensil"

And "para" is usually for living things such as 1. Doctors = Para Dokter / Dokter - Dokter 2. Dogs = Para anjing 3. Men = Para pria 4. Women = Para wanita

Hope it helps

If you mean "his pencil is black and red" I agree