This is a long one.... First off you do NOT need to be a resident to own PGYan real estate. any person or entity can own real estate. They will need to be present personally to sign paperwork with the attorney to start and then end the transaction.
No real estate agent is needed, in Paraguay the buyer and seller can sit down and negotiate their own deal out and have the attorney write out the terms and agreements. If language is a problem a certified translator or personal representative for yourself should be hired to work on your behalf. There is no recourse to your bad negotiating or lack of understanding, therefore unless you're fluent in Spanish I'd have someone on your side to assist or work with a trusted partner who is under your employment.
Do you need a lawyer to be involved, in a word no. Paraguay has escribinia's who are akin to paralegals and can perform all the same acts and functions of a lawyer for a fraction of the cost. We have personally used both attorney's and escribinia's and outside of cost there is little difference between the two. I would recommend using someone who has dealt with foreigners before and has experience in that arena as their transactional logistics and concerns are different than locals.
Depending on the type and use of the property in question special permits may be needed, having a great transactional team by your side will help smooth this one over.
Paraguay real estate is great as the paperwork involved is minimal and most transactions are done in cash. It is common to put 50% down payment when completing the written contract portion and then 50% when closing the transaction. As always make sure that you have experienced qualified professionals on your side, the kinds of professionals that provides