Worth replacing water heater - plus other questions

[Elizabeth Lee]

Thank you all in advance! I have a six unit multifamily in the South Bay area in southern California and am contemplating changing out the water heater. Currently it appears that a 50 gallon gas water heater is supplying the units (with a 40 gal supplying the laundry room). We got this outrageous quote $4800 for a 100 gal heater and have some questions since we live up in Oregon and I have never heard of the cost being so high. 1. Is this a reasonable quote if it includes everything but the permits (plumber says in SoCal no one pulls permits for a water tank)? 2. Is it necessary to get such a big tank (we did have tenants complain before about hot water running out quickly)? 3. Is it true no one down there pulls permits for a water tank? 4. Any plumber/HVAC tech referrals we can get from any of you?