Law firms can be quite successful without a formal office. If you meet clients, then you need a place to meet them that is appropriate. You can rent a conference room or space in another firm for this purposes. That way you can seem to have an office for those who require it, but you don’t have to pay an absurd amount to have one.
Obviously the technology is crucial. It is easy enough, these days, to set up a completely virtual office. Just make sure you invest in reliable and appropriate technology with plenty of security and backups.
A lot will depend on the size of the firm, how people work together when they are not face-to-face, and of course any requirements of the state in which you practice.
The main issue is that as the firm grows and needs to hire staff, the ability to trust people to actually do their work from home will come up. Some people work very well from home or a home office. Others do not. That you can evaluate with time and necessity. When the time comes that you might need someone to take calls, there are plenty of services you can use which won’t require you to hire staff, so you can delay the issue for quite some time.