A couple of salients things to note:
If you add custom column(s) to your base Quote and Order tables - you (potentially) risk problems during future upgrades (major/minor versions) of Magento.
The background process (well - technically an OOTB M2 observers) that copies data attributes from Quote(s) to the Order(s) objects may not auto-copy custom data columns (i.e. without you overwriting the observer classes to specifically do so)
That being said - here's a 20,000 ft view on how to go about this requirement the Magento "recommended" way:
(1) Create EAV attribute(s) to store the custom data associated with the Order and Quote objects.
This will involve creation of a
Setup/UpgradeSchema.php and perhaps even a
Setup/UpgradeData.php as well (e.g: in case you need to populate data for priors orders/quotes)
[ I'm assuming you already have a custom-module in place. Hence the upgrade route instead of the install route ]
(2) Setup Observers for the Quote and the Order
The specific event that you will "observe" depends on at what point during the Quote object lifecycle you want/need/wish to source and store your custom attribute(s)
For example, if you want to do so during the add-to-cart process perhaps consider observing the
checkout_cart_add_product_complete event / or if you want to do so after successful order-capture perhaps consider observing the
sales_order_payment_pay / etc.
The same thing applies for the observer you'll create to source/store the custom attribute(s) associated with the Order objects as well - For example, during Order creation / Order Fulfillment / etc.
I hope this helps get the ball rolling! :)