HTML viewer for IFrames -- help me fix the last 10%

I am an architect trying to hots a portfolio of work online, rather than sharing a printed book. There are multiple media types in this portfolio, so I have output each page in InDesign as an HTML document, and have written a small web-viewing application to click through the pages. I am having a little trouble getting rid of all the bugs, and need someone to help me resolve a couple things:

1. Scroll bars appearing on some iframes, probably due to a scaling issue
2. I have figured out how to dynamically scale the iFrames based on the window size, but I'm having trouble getting them to be centered in the window
3. delaying the display of iframes pages until all elements load

Please let me know if you have time to help me. You can find a working copy of my application on CodePen:

https://codepen.io/asp2150/pen/xxZvZvQ

Thanks!

Alexander