Updating an existing Quotation Tool written in php

Updating an existing Quotation Tool written in php. Updating the zoho api from api v1. To api v2 and adding a few features like , pulling exchange rate from a zoho crm custom module via api and updating local cache table in db. Pulling zoho crm user settings via api , getting his pricebook settings (text field name) and then pulling the correct pricebook via api. Applying discounts based on settings in the accounts module (also should be pulled via api).
minor design changes like removing fields from a table.
also developing a function that will pull latest rates from currencylayer and update a CRM module.