Architecture for a site with many thousands of nodes

Hi all.

I maintain a site based on Commerce, with several thousand unique products; user manuals. I designed it myself, wrote some modules to fill gaps in functionality etc. Everything works great. The Drupal site sits on a subdomain, and the main domain is an encyclopedia of information about the companies and machines that we sell manuals for. The main site isn't made with Drupal - it has been written in Word and Publisher since about 1998. There are also many hundreds (possibly 1-2k) pages on this site.
We are now at the stage where we would like to Drupalise the main site to improve its appearance and make it easier to manage. Impressive though it is, the menus are all hard coded and it looks as though it was made in Publisher 2000 (which it still is). I'd also like to advertise products within the information we provide, add adsense etc.
Each page consists of text and images with captions that include HTML, and many pages alternate between the two so simply using image fields on nodes won't cut it.

I've had a crack at this using the Paragraphs module and have come up with exactly what I need, but there are a couple of things that concern me - namely performance and futureproofing, Firstly I'm worried that having spent hundreds of hours migrating content into Drupal, the database will be so huge that performance will suffer or backing up will become impossible. Then there is the potential issue of migrating the content out of Paragraphs in the future - things change in Drupal all the time. I'm building in D7 and Paragraphs exists for 8, but will it definitely exist for 9? Is there some other module or set of modules I should be looking at for authoring this kind of content?

There are other issues I've yet to solve too, such as dealing with all the inevitable broken links.
Any words of advice from someone who's undertaken a migration of this scale, or has stretched Paragraphs to its limits would be really appreciated.