The fastest way to get a good landing page up is with a template. That way you don't have to start from scratch each time. Just load the saved template into your website builder, then change the headline, photo and copy to match the offer.
If you're using Wordpress, WP Beaver Builder is better at making responsive websites than any other landing page builder I've used, and I've used plenty! It's like desktop publishing for the web, with near pixel perfect placement of design elements, and total customization over the look and feel.
If you use Rapidweaver on the Mac, I suggest skipping the normal templates and going for a free-form framework for drag and drop simplicity. After looking at them all I chose Foundry to make beautiful responsive landers, that look exactly how I want.
I don't recommend using a third party service for the landing pages. If they host them all in the same place, it's easy to pick out your ID number or username, then use Google's various search commands to reveal your entire presence on the service.
If the landing page is stored on your site, you can set retargeting cookies. You get several chances to sell the product, including on the lander, with display ads in the sidebar, or if they click around on your site and leave on another ad.
If the merchant sales page has testimonials, go ahead and snag a few for use on your lander, unless they prohibit you from doing so. Just don't go making them up if they don't exist, because that could lead to fines, or worse.
So if you haven't already done so, get the Legal Forms Generator from internet lawyer Mike Young. It's so easy. Just enter your company name, address and few other fields of info, click a button and get all the legal forms, ready to copy and paste into your website.
If you don't design your own life plan, chances are you'll fall into someone else's plan. And guess what they have planned for you? Not much.