Magneto 2.1, need three plugins/extentions -- 2

1. Calculate quantities for clients. We sell by the box, and our products are priced by the box. However, we need the client to see price per square metre. This is because each box doesn't necessarily hold 1sqm. When the client puts in the required area in sqm, the quantity box needs to populated by the number of boxes they need to cover this quantity. 2. Request a sample. I need to be able to allow my clients to order a free sample, without creating any new products for this. Each sample order needs to be treated as any other order, so we can then chase who has ordered samples and so on. 3. Pay a deposit. We don't stock everything we sell. We have normal stock items, and special order items. If a product is a special order item, we need to allow the client to only pay 50% of the balance, with the remainder to be paid just before we deliver the goods. One of our competitor's website which runs on magento is http://firedearth.com. I'm not sure how many of these concepts they have on their website. There are a number of plugins available for older versions of magento, however, not for 2.1.1