GSTR - P&F, Freight - HSN / SAC Code

SCENARIO: Assuming a single tax invoice is made on sales of three items in the tax slabs 5%, 18% and 28%. P&F charge and Freight charge need to be added. Also the goods are sent via a transport provider on TOPAY BASIS and the recipient pays 900/- while taking delivery of goods.

QUESTIONS:
1. Is there any specific MANDATORY PERCENTAGE to calculate P&F charge, else can we mention any reasonable amount towards packing.
2. what is the HSN/SAC for P&F to be filled in GSTR 1 and GSTR3B
3. what would be the GST RATE applicable on freight charge with three different GST rated items.
4. what is the HSN/SAC for FREIGHT to be filled in GSTR 1 and GSTR3B
5. Will the amount of 900/- paid to TRANSPORTER while the RECEIPIENT is taking delivery of goods should be keyed in GSTR or just treated as INDIRECT EXPENSE. Can I claim ITC. Please highlight or provide suggestions, if there are any relevant answers to this 5th question.