When renting a flat what should you look out for ?

Do you guys have recommendations on websites and things to look out for flats for foreigners (University student)

I am looking for to move into an area like Tachikawa with a 20-30 m2 flat ?
Upfront Costs like deposit, key money, agent feel,guarantor company fee.

What is reasonable ?

What about the ongoing Costs like the Monthly rent / Common service fee / maintenance
Is a fire insurance required ?

What about the landlords that ask for two months rent upfront ?

Thank you for your help, I just moved here and it's my first time moving out on my own as the student dormitory living condition is really inconvenient