Okay so first of all, longest feedback I've gotten so far and I'm all in for it. I'm trying to take in all the feedback I'm getting and then I might be updating the game with everything I have gathered after the game jam so a comment like yours GREATLY helps me out.
You have a lot of cool ideas that I hadn't even thought of myself before, such as the tower tooltips, having upgrades be in a tree instead of in order, hover tooltips and the damn speedup being toggle and not hold (I have no idea why I designed it to be that way..). These are all changes I'm probably going to make if I have the time. A complete overhaul of the upgrade menu would maybe be something that I could work on. This would also allow me to add stats and other nice elements to know to the upgrade menu and just generally clean it all up a bit.
I have had the suggestion to make some kind of popup so you know what's coming during the next wave so that's definitely on the list too. The lightning tower was also one of the more forsaken towers if I can call it that, so I'm going to give it some more love in the future so it's actually clear that it can hit everywhere. (Also you are correct about the bomber, don't place it, it's incredibly weak. Mainly because of how targeting works right now)
Good idea about communicating the not being able to build in the storm thing. I might just put that into the tutorial too, it's only one extra line for Bert.
I'm really glad you enjoyed my game it really means a lot to me to see people play something I made and enjoy it to the fullest! Thank you lots for this big feedback comment. I'll put your feedback to good use to become a better gamedev (and maybe make my life in uni easier so I can gamedev more TT).