Great question here. First things first, as an SEO/growth marketing person I need to point out that unless you are creating these pages on the scale of millions, you're not going to be flagged for spam. In fact, even if you did create them on that scale, you still wouldn't be flagged for spam; you just wouldn't get the organic traffic to them that you'd want because your domain probably isn't strong enough to support all of those pages.

Here is what I recommend:
1) Think about your site as an ecommerce site. This is how you will want to structure it. Think homepage > categories > subcategories > product pages. If you buy many different types of printers, then something like homepage > Printers > Inkjet Printers > (specific inkjet you buy) if you want to get that granular. You have to do the keyword research to figure out how deep you want to go, but this is the way to think about it for SEO.

2) Any halfway decent CMS will allow you to create pages at scale to target different keywords. Wordpress will let you do this, Joomla will let you do this, Squarespace will let you do this. If you need to create them at a huge scale, often that can be done via the database (uploading the content and specifying the URL/title/H1/H2 etc for each page)

3) It's ok to use a page template for your different page types (eg category/subcategory/product page). When I think about it, does anyone these days *not* use a template? Anyways, you should also ask yourself "How can I make these pages as unique and relevant as possible from the others onsite?" Many people start thinking "how unique do I need to make these pages so I can get away with ranking well and get sales", but that's lazy thinking. If you're really looking to add value, think about how you can make them as unique, relevant, and valuable as possible.

By the way, I disagree about using either Unbounce or Optimizely for this. Optimizely is an A/B testing platform and Unbounce is great for one-off landing (aka "squeeze" pages) and testing them, Neither is suitable for this project.

Good luck!