|If your friend has the skills to write their own software to handle this enterprise surely they would have some idea about the hardware requirements? What exactly are you asking about?|
I would suggest your friend needs a comprehensive business plan and would benefit from establishing a relationship with a nearby specialist IT consultant who can assist with establishment & control of the database.
No doubt the client medical practices will require comprehensive reports including aged debtors, statistical reports, arrears & debt recovery data. It is also very normal for medical practices accounting systems to interract directly with health insurance providers/government public health funding authorities etc. Such software already exists and your friend may be trying to re-invent the wheel.
Then there are the login needs, Security requirements, Data throughput requirements, backup provisions ( Offsite is best)
Privacy provisions etc, the list goes on.
"what all would be needed for this?"
Much more than could possibly be conveniently conveyed through this forum.
Goin' Fishin' (Some day)