Where can I get a version of Bluefire Reader what works with iPad 1st gen, iOS4

If it's not in the App Store, you can't download and install it.

The iPad 1 can be upgraded to iOS 5, which would meet the requirements of the App.

Any reason you don't update to iOS 5? That way the current App would work on your first gen iPad.

Other than that, no, there are no external sources for Apps . All app's available versions must be obtained through the App Store.

No real basis for that. The upgrade fixes issues and glitches in iOS 4, and should prove to be more stable if anything.

Battery life is extremely relative. It can drain faster if you do many things, or slower if you do nothing,

I noticed no change in performance on my Gen 1 iPad after upgrading to iOS 5. is still running fine. Any battery performance decrease can simply be chalked up to age. Not necessarrily something iOS 5 did.

Remember also that you only hear the about the bad stuff of something,. hardly anyone ever posts to say how great their device is running with iOS 5. Also in the grand scheme fo things a few problems are to be expected. When over 8 million first gen iPads were sold and only a few hundred show issues with iOS 5, not upgrading because it "might" have issues is just silly.