MENSA member, CS degree from Notre Dame - how practical to make a successful iPhone App?

So I'm learning Swift hoping to make iPhone apps and I mention my creds to show that the intellectual barriers of programming is not a problem

my question is, how successful can you be on the app store? For instance, say I had a moderately good idea for an app and created it - could I expect to make, say 1,000 or 2,000 dollars per month from it? How many people make at least 1000 per month with their app(s)?

Am I being tracked by my ex?

Recently I have noticed that on my iPhone in Settings>Privacy>Location Services>System Services that next to the Find my iPhone app it has a grey arrow next to it? At the bottom of the screen it says "a grey arrow indicates that an ITEM has used your location in the last 24 hours". Does this mean that someone is logging into my account to preview my location or could it simply be my phone updating its own location? The only person who knows my find my iPhone information is my ex so it would be helpful to know if anyone has any information?
I would like to also note I have not used the find my iPhone app in any way in weeks maybe even months. TY!

I deleted iCloud account before I erased the iphone?

I deleted iCloud account before I erased the iphone?

Added (1). Can I get an account that I deleted on iCloud back?
I lost an iPhone 5s which did not have find my iPhone enabled! I freaked out so went to my service provider and got the Sim frozen and got a new iPhone and new sim. I then deleted my phone's iCloud before I erase
as I thought that deleting the iCloud is the way to erase it?), all I want is to make sure no one uses my photos and my personal info, please help!

My picture's colors look different on pc vs phones. I want to print it on a poster, how do I know which one the colors will come out like?

Basically I drew a picture on my laptop with FireAlpaca for a friend. Let's say the main color is a dark bluish purple, how I wanted it. I saved the file and sent it to my phone (iPhone 8+) but the colors appeared more pink/reddish purple. I tried a few other devices (iphone and Android) and the colors were slightly different for each one. I wanted to print the image on a 20 x 30 poster at Walmart or with UPS, for around $20. I want the original dark blueish purple color, but how do I know that's how it will come out? How do I know which one the print will look like?

I would just print a smaller version for cheaper to test it but that would mean waiting for delivery, hoping it comes out fine, then ordering the actual poster. (Picking up the image instore isn't an option due to transportation issues) If I do that though it won't be here on time for the birthday.

Any advice on how to go about printing?

Separate MANY contact phone numbers on iphone?

I recently inported my contacts via i cloud and for some reason it imported all my contacts phone numbers into one single contact and it has all the names blank is there a way i can just select like 5 numbers and add them to a contact to at least organze them by groups (i had like 180 phone numbers saved i do not have the time or patients to redo all of them)

How to turn off Apple send messages quietly?

I turned on the send messages quietly mode by accident, and now I can't turn it off. I don't receive any text notifications, and going into the notification settings and changing stuff doesn't help. I have an iPhone 6s if that helps.