The zoomed text editor is that little cross in a square icon that you see in multi line text input boxes, like the one you used to write the message on the forum. Click it, and a resizable window appears for typing in. Not only does this give you more space, but it means you can use keys like tab that you can't in the input box. I use this a LOT!
As for subscribing via Endo, I just drag the url from Omniweb onto Endo's dock icon. Endo then looks for feeds at that URL and gives you a list of what its found for you to subscribe to. Omniweb does desperately need a preference to allow people to send feeds to their news reader of choice, although it does respect any feed URLs using the feed: protocol.
Here's a few more of Omniweb's features:
http://www.hicksdesign.co.uk/journal/omniweb-tricks