Hello Kapil,
Your questions has covered most of FX process.
I'll try to answer few of your question.
Answer 1) The process is correct, Its based on what your company required consultant has customized the system in that fashion, As you said there is not posting even during maturity of deals, that because in customization setting is missing for posting. Incase its required please consult you consultant to make the changes in system for Flow type-(here relevant for posting is unchecked).
Answer 2 & 3, I'm not sure why consultant has suggested to use such a lengthy process to settle early deliver deal, There might be some reason for the same. Please check,
But the same process can also be addressed, throught FTR_edit and settle the single deal through cash settlement.
Also note, 103 is only used for netting which means you are trying to settle couple of deal together and that can be excluded if you have only single deal.
Answer 4) TPM18 is used to do the valuation after the deal has been closed.Realized gains and losses are determined according to single valuation of transactions principle. This is calculated by taking the difference between the forward rate based on the conclusion of the contract and the posted rate on value date.
Let me know in case you need more information.
Regards,
Jaiin