I don't think you have anything to worry about. I think your grate steel temp will be a lot higher than the temp those springs will ever reach, unless your coals decide to start leaning on the door. You could always shorten the springs if you get bored. :o) I do prefer the heavier/wider opening grating like you used for the firebox, if I had some, I would have rather used that instead of the expanded metal that I used. Bottom line: Cost, I already had the expanded metal from other projects, so I just repurposed what I had. The framing on mine is bed framing made into a angle iron tray with 4 post-style legs welded under it, which is made from scrap rebar I ended up with from a friend. By doing a free standing frame, I can remove and rework the idea until I am 100% happy with this portion of my build. (I saw some V shaped frames that auto-feeds logs, insert drooling mouth here, maybe some day will play with that idea)
Keep up the good work!