Advanced Mailmerge Template for a standard agreement

Would like a document in which it would prompt for several things and fill in the necessary fields automatically for a standard sale and purchase agreement. It will also insert the necessary pre-set clauses depending on your answer to the questions. I know this can be done via MailMerge and fill-in but fill-in has certain limitations (such as 255 character limit?) and I understand this can be done via VBA and mail merge events? Some Variables: Vendor Vendor Address Purchaser Purchaser Address Whether Vendor/Purchaser is a company or not (and to replace it with the appropriate signature boxes) Property Description Is the property free from encumbrances? Purchase Price Deposit Amount Balance Purchase Price Whether there is an existing charge? Should the Deposit Sum or the Balance Sum to be used in discharging the charge? Is Real Property Gains Tax payable? Whether Vendor has option to abort deal by paying back Deposit and a like sum? Who should bear legal fees? Who should bear stamp duties? Also would like instructions on how to do minor edits. A sample of the document is attached which shows the kind of variables involved.