I'm Miles from the Social Care team at Shopify. Who doesn't love a sale? A tiered discount is a great idea, and I'm happy to point you in the right direction to help you achieve this.
At the moment, Shopify's built-in discount tool is simple enough for new users, and has some awesome features for the pros. With that, there can be a shortfall on features. Whilst you can create an automated discount or "Buy X, Get Y", it's not able to tiered at the moment using our discount tool. It's something we've received a lot of feedback about, and I'll be happy to add this post into the feedback so our team can consider it.
With that being said, this is where our Shopify App Store comes into the picture. Our App Store is full of great integrations from our partners to help fill in those gaps where we don't want to overcomplicate the platform. You'll find apps for things like email marketing, SEO improvements and, more importantly, discounts. There's some great apps that allow for tiered discounts like the one you're suggesting, and I've recommended a couple below.
These two apps also work quite well together. Bundling products, coupled with tiered discounts can really increase the customers experience. If these apps aren't quite what you're after, here's a full list of apps created for making discounts easier: https://bit.ly/357xYvM.
Once you've sorted the discounts out, let's talk about how you're going to market to your customers. With free courses on marketing, store design and more, I'd recommend checking out Shopify Compass (https://bit.ly/2LyfedE). It's the one-stop shop for merchants who want to increase their conversions and start making sales. It's free to join and free to use!
Good luck with the sale, and please let me know if you have any questions at all.