I noticed that proxying images seems to delay the start render time. Is there anything I can do to lazy load proxied images for a quicker start render time?
Proxied images just regular images. There's no real reason for them to be slower than any other image when they're cached at least. (When they're not cached, we do need to fetch the image from the source first.)
The shouldn't really be blocking, but I suppose that would be down to the browser.