I did owner financing and the buyer stopped paying. Foreclosure Flat fee in MD needed

Hi, Happy New Year! 

I bought a piece of land through a tax sale in 2011, in 2021 I sold as-is, owner financing, through an attorney. 

I have the paperwork, but the attorney no longer works on this kind of stuff. I did several mistakes like not asking for a bank transfer and instead went through paypal and cashapp. He stopped paying in Oct 2022. I did not have any money to pay for attorney fees until now and was hoping for a flat fee. I can do some leg work to keep costs down if necessary. 

He said he wanted a space to take his RV and camp for a few days, like 4 months later he decided to call about perk and failed and then wanted his money back, even though it all went to attorney fees. He paid for about a year and then stopped giving excuses left and right. He is a criminal attorney and charges $350 per HOUR of phone consultation and the MONTHLY mortgage is $255. 

I'm not saying anything about how much he charges, just letting you know, that he can make that monthly payment in less than an hour. Now I find out he didn't pay the property taxes. 

In the meantime, should I pay the property taxes? I know it would still have to go to tax sale and even after that I have 6 months before foreclosure proceedings starts. And it might not be bought based on it being unbuildable.

Also, what kind of certified letter should I send out? Breach of Contract? Late Mortgage? Something else?

I don't want to do this solo but I have limited funds that I had to borrow to get, so if there is anything I can do to lower the cost, please let me know and I will try to do.