1) is it a leasehold property? if not, then why the need for 5 months? Transmission and Transfer can be presented simultaneously and the transaction can be completed with the period of a normal sale and purchase agreement.

Bank's letter of offer usually have a validity period when the offer will lapse, check with your officer and tell him/her the circumstances, if need be, the bank will issue a supplemental letter of offer to extend its offer.

2) since there is a transmission going on here, the 90 days period to pay shall only commence from the date the Transmission documents are in order to be presented (if the property is a freehold) or from the date the consent to transfer in your favor is obtained (if the property is a leasehold).

Please don't be lazy and trust the solicitors will do everything for you, it's your money so be aware of how it's going to be used. Comb through every terms and ask the solicitors if unclear and don't go back threatening the solicitor if something goes wrong. Caveat emptor, bro.

3) Anyway, whose solicitor are you using? Please don't tell me that you using the one recommended by the vendor because although in record, you are represented by them and you should be protected, in practice, firms will protect the people they are acquainted to.

4) Sure you can cancel the booking, read the offer form the agent passes you and see what is the consequence of cancelling.

Keyword is "READ", read everything before you sign because any documents signed is valid and binding. Not even the courts will accept "i'm illiterate" as an excuse to void a contract.