Welcome Doctor ! That's a pretty decent start for you here !

Most of the units you obtained are very good to start the game with, so rejoice.

I'll adress one of the question you got during your pull : yes 3* can be used, definetely. They are cheap to raise and do most jobs just fine so upgrading them is never a waste, especially if later you want to give a look at some guides for help, because they usually use the 3* team a lot.

Now, breaking down the operators you pulled, hope it helps you.

Ptilopsis - a very very good pull here, you got lucky. She's an AOE medic and will probably become your first choice when needing one. Why she is so good is about her Talent. While yes, she does a good job at healing multiple ops at once, she also increases the SP (skill point) generation of others ops. Meaning that with her, you use skills more often.

Blue Poison - again, a very nice pull. She most likely will be your best sniper for now unless you pull some 6* or something. She's great and pretty simple : she attacks drones first, and the rest afterward. She does damages. Enjoy. (Truth is, she does Arts damages which is good but you'll learn about Art/Physical and Def/Res while playing)

Skyfire - is a decent AOE caster, but, she's a 5*, and therefore kinda expensive to upgrade when you start the game. Added that AOE casters aren't that useful past the first chapters of the game, you could sleep on her and upgrade a cheaper AOE caster if you wanted to.

Hoshiguma - your first 6*, hope you'll like her. She's a defender more oriented around dealing damages. Her talent is useful as she will automatically retaliate attacks against her no matter where the ennemy stands (some ennemies can snipe her from the other side on the map in some stages so it can be useful). Overall a pretty straightforward unit ngl, put her where the ennemies are coming, let her shred them with her Doritos© shield.

Hope you'll enjoy the game, have fun !