2004 2.4 Harmonic Balancer

I have a 2004 2.4 Tacoma needing a harmonic balancer now that the slight rattle on startup has gone to a full-blown 20 second cacaphony. My mechanic thoughtfully supplied a $638 estimate which shoild cover his boat payment. Obviously dropping this much money while I can do it isn't an option. I do have a few questions hopefully the community will be able to answer.

1. I see 3 pulleys but all replacements I see have one pulley. I am guessing the old ones bolt to the new but mechanic is also replacing one of them as he thought it a good idea. I am I correct in assuming all dampers are sold as single pulley? Car has California emissions BTW.

2. Is it a good idea to replace the crankshaft oil seal? It is not leaking now.

3. The prices of the balancers are all over the place. Dorman makes one that is supposed to fit the 2004 at $35. The model number on the estimate (13408-75030) is available from Rock Auto for $80. The gold plated model with Swarovski Crystal accents my mechanic wants to use is $266. Any recommendations?

4. He wants to replace the crankshaft bolt and the 4 damper to a/c pulley bolts as well. Is this a good idea?

Thank you in advance.