how to arrange a amateur tournament


That completely depends on what you are willing to run and what the local players want. With 30 players a 5 round swiss style tourney should produce a clear winner. If you do a rapid time control you could do the whole event in one day.

This gives an overview but there are probably other sites with more details
https://en.wikipedia.org/wiki/Swiss-system_tournament


You mentioned you were U1500 rated so....
Anyway, anyone that has a rating, use that. If any of them have played each other before you can assign some ratings, if you can feel confident in your strength order. Finally, just assign the rest of the players a random paring number and use that as for the paring order in the later rounds.