Hi Rahul,
1. If goods are not under duty-suspension, no special documentation is needed for the journey - just the same as a domestic delivery.
2. As far as I can see from the code, you can use GTS to create (only) Transit documents from the transfer of SD Billing Documents. You would need to code the "CTRL" BAdI as previously explained, in order to force the transfer for EU destinations, and I think you would also need to use BAdI /SAPSLL/IFEX_SD0C_R3 to set up the "Transit" situation, by setting field HEADER_CSD-CUST_PROC to value '01', and possibly also setting field SRVLL to value 'LECTPR'. Please try it, and let us know the results.
3. Yes, I think the TIR Carnet scenario should be ok.
Hope that helps.
[By the way, please don't start a new question with "Hello Dave". Others may also want to answer (and indeed others often have better answers than me), and I cannot guarantee to provide any answers or assistance in this forum - thanks Image may be NSFW.
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Regards,
Dave