What does TBN do with the 'seed offerings' that their constituents send them in the hopes of buying God's blessings? 

According to the Orange County Register part of that blood money went toward the purchase of a:

The 9,467-square-foot house, set on over an acre in the guard-gated Harbor Ridge community...the house has its own large gates, six bedrooms, an elevator, private tennis court, swimming pool and spa and a grassy pavilion area with an outdoor kitchen. In the foyer, a chandelier hangs from a high ceiling. Interiors include a formal library, piano room and bar.