General

Offices
Do you need them? (it?).
Probably not for a startup ISP if you can reasonably do everything from an existing and available home office or business.
It may be useful to separate the technical needs of the ISP from its business needs. Somewhere to locate the computer equipment and have data links connected into, modems and phone lines installed etc., need not necessarily be a business office location. A 'Computer Room' may be a good idea and locating it in a room adjacent to your business office can have the advantage of centralising the whole operation and it is nice to show-off your technical equipment to visitors.
However, many startup ISPs manage to run their business from a residental location and avoid the initial setup costs of moving to business premises. In a home-office location there is also the added advantage of having someone present for more hours per day than just normal office hours.
In any case, whether or not to locate your ISP business in a business location is very much a personal decision.
Some factors that may influence such a decision:
Availability of phone line pairs, try to guesstimate what your needs will be here in a couple of months and in a years time.
Space for growth, if you need to bring in people to help run things, help desks etc then is your present location suitable, can you take more space if needed?

Hardware