Thank you for your input!
I based this one HEAVILY off of how a kirby level would be made, mixed with how much fun it is to find secrets and bonus rooms, even if SMM doesn't have a means to hide them really, really well.
I'm planning to re-upload this in a few days (seeing how it's the only way to avoid having it slapped with a perma-ban tag if deleted) as soon as I can get enough time to re-balance the enemies. Ideally, it'll be noticably easier, with a way to get a line of kills (200, 400, 800, 1200, and so on with a koopa shell) with almost any enemy, and if not a way to bypass them completely; but it will still be a level that will make you work for that goal jingle.
Originally, in that bowser Jr room with the bomb-ombs, you were going to be sent into a cagematch with him while the pipe amply supplied you with mushrooms, but I would be left without enough pipe exits to get to the goal, so I thought it would be funny to watch him be sploded. Later on, there's a point where you can battle him for real, with an emergency exit to the arena and the ability to skip it completely with a lakitu cloud.
I'm also going to toy with the coin positions to see if there's any positions that are more fair and not too drastically different. In the meantime, I'll tell you how I got all 5 while testing as thanks for being such a trooper in the level and reading this.
1: In the bowser jr room, clear the enemies with a cape or the first shell, and wait for the paragoomba to come from above. In plain sight. Mind the fireballs.
2: Use a shell to take out the lakitu and fly up where the arrow points. Watch out for the spikes and falling cheeps :^) If it helps, the most ideal time is JUST AFTER they are about to crunch. Get the nearby checkpoint after this.
3: Find a P-Switch and go through the P-Switch door. Straightforward. On your way back, you'll be at that conveyor belt place. Run and jump to get it, and if a spring throws you back, try to get a jump in so you land on the donut blocks.
4: Guarded by Hammer bros. The most reliable way to dispatch them is with a shell, fireball or a POW block found somewhere before hand. Also, one of the blocks on the bottom, to the right of the hill has a star if you are daring.
5. The Farthest to the right you can go over the big hill, right after the hammer bros.. There's another Lakitu that spits goombas just before. Mark his deliveries "Return to sender" and use the cloud to dodge the chomp, dip in the bottom of the "valley" and fly out. The Dizzy effect, should not be too much trouble if you are still big mario at this point.