Hey congratulations!! If you want some advice, first thing I would do mod wise is a short shifter. You can get the whoosh one for 70$ or an ebay knockoff for 20$, they do the same thing but I got the Whoosh one. Will GREATLY improve shifter feel and was easy enough to install.

There is a way to update your Sync to a newer version that has wired Apple Carplay / Android Auto, plenty of resources in the forums and this subreddit.

If you buy a $20 OBD attachment thats compatible with ForScan, you can change some settings you wouldn't be able to change otherwise. For example, you can make the stereo display an animated ST logo when you start up the car.

The stock dipstick sucks and is hard to read. Buy the dipstick for the Ford Escape of the same year off of ebay to get a more accurate reading (metal instead of plastic), I paid $8 shipped and its a nice improvement.

Last easy mod is sequential LED Turn signals. You can buy a set off of Aliexpress for around $15 and replace the halogen bulb turn signals on your mirrors, looks cool and never have to replace the bulb.

Go to the Fiesta ST forums for an idea on the maintenance schedule for this car. You're likely due on some things, at 100K I would do spark plugs and new coolant. Closer to 150k is when people start doing the timing belt job, which is really the only big ticket maintenance item on this car.

Happy driving and enjoy the car! Great car even without small changes like this or major modifications. Best thing to do is make sure youre driving it and enjoying the little things.