Power supply for DSLR, Star Adventurer and dew heater strap

[janesdsg]

Courtesy of the lockdown, I'm dipping my toe in the AP pond and have got myself a Star Adventurer (thanks Stu1smartcookie) and Canon EOS 80D body (fleabay). I'm hoping to use a couple of pentax-k prime lenses with the Canon (adapters in the post), and am buying a W&W Astro dew heater strap to use with these. Also on the "to buy" list is a dummy battery and dc coupler so that I won't be relying on the camera's battery:

https://www.amazon.co.uk/dp/B07Q51DZPZ/ref=gno_cart_title_1?_encoding=UTF8&psc=1&smid=A2W9IV2WHKJZJ

I'd like to power this lot with something like one of the anker power packs that get a frequent mention on SGL but despite many hours reading on here, picking up lots of useful info along the way, I'm no nearer deciding which power pack will do the job.  It looks like I will need four USB outputs (one each for the Star Adventurer and dew heater strap, and two for the dummy battery and dc coupler in the Amazon link as this has two USB plugs). Is it better to use two power packs with one solely for the camera, or look for a power pack that has four USB outputs?

Something else I'm unsure of is how I go about not exceeding 8.4V or risk damaging the camera.  This probably sounds really stupid but if the power pack is 5v, would using two USBs slots double that to 10v.  (That last sentence will give you a good idea of my lack of knowledge and why I'm confused about this 🤔.)

I'd be very grateful if someone could point me in the right direction.

Jane