What is the difference between "circa" and "so gegen"?
If there are other words like these that you could recommend to me as well, please do so! :)

Question

What is the difference between "circa" and "so gegen"?
If there are other words like these that you could recommend to me as well, please do so!  :)

Answer

Hey Zachary,

'so gegen' is mostly used if you speak about time.
When did you meet? - About 13.00 o'clock. 
Wann habt ihr euch getroffen? - *So gegen* 13.00 Uhr.

'circa' is can used just as 'so gegen' only by using 'Um'
When did you meet? - About 13.00 o'clock. 
Wann habt ihr euch getroffen? - *Um circa* 13.00 Uhr.
Additionally:
You can use 'circa' in any situation in which you are do not need to be specific - You can translate is as 'approximately:
How much money do you earn? - Around 50€
Wie viel Geld hast du verdient? - Circa 50€

I hope this helps!
Best wishes,
Johannes

Answer

"So gegen" is informal speech, whereas "circa" is more used in writing (and usually abbreviated as "ca.").

Answer

"Ungefähr" 
Im Zimmer sind ungefähr 25 Personen. 
Etwa
Etwa 20 Personen kommen morgen.
Wir können uns etwa um fünf Uhr treffen.