If you are familiar with the board game "Go" that is popular in China and Korea, there is an expression: "Lose your first 100 games quickly." If this is your first composition it's a great first effort, but don't have any expectations of success for your work at such an early stage. Just write, and you will learn from the writing. You're going to lose the first 100 games no matter what you do. You don't know the right things to think about yet that would help you win. So don't take too much time to think for now. Play. Enjoy yourself. And the knowledge will start to seep in from the experimentation.
I could definitely recognize the bird songs in your piece and enjoyed them.
To combine rests in musescore, click on the first of the rests to be combined, and then select a higher note value from the palette at the top of the page. The program will automatically combine the next few rests to make up that note value.
For the tempo markings, you can specify them exactly as you did, so the playback will sound precisely the way you want it to, but then "hide" them, so that they will not show up on the pdf of the score, or when a paper copy is printed. Use the dropdown menu to open the "inspector." Click on the tempo marking you want to hide to select it, and click the checkbox that says "visible" to make it hide or reappear. It will still be visible in the score while you are working with it, so you can make changes later if you need to, it just won't print or show up on a pdf that you export.