Is it safe to have chelation therapy on a regular basis?

Yes. Most of us who provide IV chelation therapy recommend 1-2 treatments per week, for a series of 10-30 treatments, or until the desired benefit is obtained (usually 20-30 treatments), followed by monthly "maintenance" treatments thereafter. Adverse effects are rare, if kidney function is normal--and kidney function generally improves with proper dosage of edta.
Chelation. It is very important to only do chelation with a physician who is knowledgeable and experienced. It is only safe with close careful supervision and management.
Depends on technique. Chelation is a broad category that ranges from intravenous infusions to simple dietary changes. What you are trying to chelate dictates the approach and how aggressive you will want to be. There are many time-tested protocols but few rigorous studies to prove their effectiveness. As with all complementary techniques, choose your practitioner carefully. Educational pedigree does not equal skill.