I am wondering if more vouchers/coupons with free advertisement credit (e.g. 50 EUR + 35 EUR) can be applied to a new Google Adwords voucher in the initial 14 days period ? Is there any limitation on the type of voucher that can be used ?
No, you can only use one voucher per account so make sure the voucher you'll use is a good one (£100 is currently the highest as far as I know - note that it's £100, not $100)