Hyperdb Multiple Database servers?


So I am getting ready to possibly take on a pretty large WP site. I would like some feedback if I should avoid this for WP or if my plan of action would make this setup work and also have a couple of questions.

Website Specs:
1. Information Side:
- This part of the site is strictly for info about the company. This will be 90% just static pages, a blog, and calendar.

2. Ecom site:
- This site will run very few transactions.
- This will be installed a sub-domain
- This will have roughly 150,000 products (this is what I am most concerned about)
- Mainly used for a product catalog
- Will run through WooCommerce with assistance from Gravity Forms & Advanced Custom Fields

Currently the ecom site they have is an out of date ASPX custom system that presents many troubles for them.

My ideas for making this work:

1. Recommended hosting: Host Gator VPS Level 7 Host package
- CPU: 4.25 GHz
- RAM: 3168 MB
- Disk Space: 165 GB
- Bandwidth: 2250 GB
2. CloudFlare Pro DNS/CDN Service
3. MaxCDN account
4. Configure W3 Total Cache

Now, the final step for hopefully being able to make this work is I would like to setup and configure the HyperDB plugin for Wordpress. My only question is, are there hosting companies (any recommendations wanted) that will host just MySQL DB's? I haven't done a setup like this yet so I am a little unclear on the HyperDB or MultiDB setup, but from what I understand I can host the 2 sites on the HostGator Level 7 VPS & part of the DB... then purchase SQL hosting elsewhere (ideally 2 servers) and split the databases amongst the 3 servers... only thing is HostGator does not provide this, and I am not getting too far searching online.

So, I just want to get some insight on if my plan above will be successful for a project of this stature, and any recommendations on DB hosting and if my theory is correct with having 3 servers to handle the load and scaling.