Hello Sahil,
AS far as I have understood your arrangement, Company A is buying from Company F in that case the importing company will be paying Customs Duty as well as IGST on the imports, it has nothing to do with you.
When we talk about your commission, whatever amount you receive from the Foreign Company as Commission is chargeable to GST as the service is provided in India.
Your third case is when the foreign company remits you funds to organise events, then it is very difficult to prove that is it a mere case of reimbursement of expenses or includes operating expenses and fees as well. It can be very easily disputed and may involve litigation. The government will obviously expect you to pay GST on the amount transferred unless you pay the bill first from your own pocket and the company re-imburses you bill by bill at a later date.
Trust this clarifies your query.
Feel free to call / get back in case of further clarifications.
Thanking You.
Regards,
Rohit R Sharma
BCOM, ACA, LLB-GEN, CERT. FAFP