As this is part time office, avoiding any extra expense is likely a key objective. If you can't live without staff at startup, an extra laptop would be needed for each staff member.
The laptop at front desk should be fastest and most expensive if the database will reside there.
If you can use existing network, wired connection is simpler, more secure and likely more reliable. Especially important for the laptop with database instance.
A wireless router for this situation is same as you buy for home. If you go that route, be sure to turn on the security, don't broadcast the SSID, & restrict to certain mac addresses. Simple best practices need to be followed.
