I suggest you engage a lawyer to check that the offer document envisages issues such as the offer being subject to mortgage availability or sale to include furniture, as the case may be. Also, the offer document should name the party responsible for payment of transactions costs (Notary fees and Land registry fees, and municipal capital gains tax).
The date of completion is important, since you want to make sure you have the funds to close the deal on or before the projected time.
I recommend you do not formally commit yourself to a seller without ensuring a lawyer has given his approval. Be safe rather than sorry afterwards.
