1 & 3 . The sale of land is exempt from VAT. However some sellers may choose to “opt to tax” the land and charge standard-rate VAT on the sale if they want recover the VAT incurred on the purchase or development of the land or on professional services associated with the sale.
2. Stamp duty is paid by the purchaser.
4. If the land has gained in value, you may need to pay capital gains tax.