Two different visas both grant 30 days, but they behave very differently. The Visa Exemption (BVK) gives a fixed 30 days that cannot be extended. The Visa on Arrival (VoA/e-VoA) also gives 30 days, but can be extended once for another 30. If there is any chance you will want to stay longer, always choose the VoA over the exemption.
If in doubt, choose the VoA — it preserves your option to extend.
Only if it is a VoA — that can be extended once to 60 days. The visa-free exemption cannot be extended.
The VoA, in almost every case, because it keeps your option to stay longer open.
Yes — your day of arrival is day one, so plan accordingly.
