Yes, we do! :) all shipping discounts are already made and automated, according to how eCrater charges for multiple items (and lots) if you're not sure about Total of your order - please do not hesitate to ask us! :)
Normally registered airmail supposed to take 14-21 days, provided there are non any delays in transit or by customs (especially in the country of destination)
By default we use regular registered airmail of Post Thailand. Unless buyer requests some other option, which can be arranged for an additional price.