Once you have added the required linked products to your quote record from the upsell window, there is no option from the quote record to access the upsell pop-up again. It would be useful to have a button to navigate back to the upsell pop-up to add more linked products from the main product added.
It would be best if the recommended upsell products and values when carried over to the word document were not included into the overall quote value (but the price needs to be shown) and should stand beneath the actual required products that needed quoting. The assumption that customers will buy the recommended upsell is not always the case and in some industries a further written quote would be necessary for actual items required.