How much can I ask for in a security deposit legally in PA?

Things I did right:1) I was able to market it well for the time I had and had a list of people who wanted in if my first group didn't send in their security deposits.

It would be no different than any other tenant - lease & security deposit. 

In the meantime we spoke on the phone about a $15k deposit upfront to lock the property up this year.

The tentative time slot will be one Monday evening each month, typically the beginning of the month.

You will need to get an estoppel letter from the tenant and signed by the landlord  saying everything is correct in the lease including security deposits and anything that was a verbal agreement( discount on rent for mowing yard). 

I am not comfortable to proceed with this purchase so what is your advice to me to withdraw this purchase agreement and to get back my earnest money deposit from the Auction company?

Their deposit was $2600 and I'm only planning on retaining their deposit, but not charging them the remaining $1000.Full story: My tenants with a 2 year lease just moved out after 9 months.  

Also there is 1 month of rent he forced me to use from his security deposit, citing covid related hardships. 8 months have passed and he has still not replenished the security deposit.What are the best legal ways I can evict this tenant?

In the meantime we spoke on the phone about a $15k deposit upfront to lock the property up this year (which is negotiable).