The same for any FFL. The biggest requirement is that you have to have a premises from which it is legal to conduct your firearms business. For your business to be based in your home, that generally means you need to live in an unzoned area, or your property has to be multiply zoned and one of those zonings must be for commercial/retail space, or you have to get a permit or zoning variance, depending on where you live. If you rent, in addition to the previous requirements, your landlord must approve your FFL-related use of the property.
For conducting mail-order work solely as a gunsmith, the requirements for off-street parking, signage, posted business hours may be relaxed, or may not be relaxed, depending on where you live and who has to approve the exceptions. ATF does not require public business hours if you specify that you will work solely as a low-volume gunsmith.
Be aware that if you choose to go the low-volume gunsmith route, and don't do any gunsmithing, but buy a lot of guns for yourself, you'll likely lose your FFL at your first compliance inspection.
Once you've got the FFL, or prior to it, but before engaging in any business under the FFL, you'll also need to have applied for and received all applicable licenses.
I can summarize from my own home-based FFL experience:
1) Applied for and received a 'home occupation permit' from the city to conduct low-volume gunsmith work, custom order guns and ammo, and do light manufacturing from my R1-zoned residential address.
2) Since I was applying for an 07 (manufacturer) FFL, had to go back and forth between the city and ATF for five or six months, and the city came out twice to inspect my proposed work areas, check that I had off-street parking (driveway) available, and set up some ground rules for me about stacking customers, foot traffic not to disturb the neighborhood, etc.
3) Finally got the city to tell ATF it was, indeed, OK for me to do light manufacturing and retail sales from my home, subject to reinspection, at which point ATF sent out inspector to do my interview, and I had my FFL in hand about four weeks after the interview.
4) applied for and received city, county and state sales tax licenses, applied for and received EIN to get my SOT No business license for a gunstore is required in my city or state, so I didn't need to get that.
Keep your bound book up to date, conduct your affairs as a business, and do your best to turn a profit. Failure to engage in regular FFL-related business activity, or consistently failing to turn a profit can get you in trouble with the IRS for tax evasion, or ATF for fraud, or just result in them declining to renew your license.