No real thoughts on the HUD. It just needs graphic design love and a better font. Nothing was irritating, it just felt small and too minimalist at the top. I understand you don't want anything in the way but at the same time you don't want it tiny and stuffed in corners.
Probably the best key would be the right control but keyboards vary so the best option would really be to let people select their own key(s).
To be fair, in modern archery no one is running around because the stance is very important. Defensive players advance slowly, systematically clear out a section, move forwards when it's safe, and like to snipe (and defend areas but there's nothing to defend in this game and that's fine). There always came a point where I had to venture out because I couldn't reach or couldn't see the final bots so for game design it would be figuring out how to place more of those types of bots and likely use scenery to help with that too.
A much as it as really helpful for me as is I think Strider should be adjusted if you want to push players a little more - maybe you can only gain health when a bot dies or maybe there are one-use health "pools" in the environment that you have to reach in order to heal, or maybe you just can't heal in the staging area so people would have to duck out a little bit, at least. It's tricky because one time I had a bot right above me on a platform (seriously, it could not have been closer - the platform wasn't even in my initial field of view and I couldn't understand why I was dying), and way too many of them on the other side, so I did have one level where I had to act particularly fast and it was very dangerous.
So... experimenting and testing, I guess. As the game stands now, though, I had a really good experience and the difficulty progression was perfect for me. And the game was fun - let's not forget that crucial aspect!