So you've got a single 60 AMP service branched into 5 panels, all of which are fuses and not breakers, to serve 4 units? Is that correct? I'm surprised that you were able to get insurance at all. You need to upgrade that service. You're opening yourself up to all sorts of liability as a single 60 amp service is no where even near code for 4 units + common areas. Right know you own a 4 unit fire hazard. When it burns your tenants will sue you and will probably win.
$8k seems high for a service upgrade, but I'm guessing that also included replacing all the sub-panels in addition to the main. I'd be expecting to spend $4-6k. Your utility company will require that your electrician pull permits and have a final inspection prior to bringing the upgraded service to your property, so make sure you hire a licensed electrician.
Having said that, a 100 or even 200 amp service is not really going to be sufficient to serve 4 units + common areas. My suggestion, if you are going to do it, you might as well upgrade to separate meters and 100 amp service for each unit. It will be done right at that point, and it will increase the value of the property.