Whether you are "selling" guns or just transferring them, you still have the same considerations a regular dealer has.
You must accept delivery from sellers, arrange pickup by the local buyers, and arrange shipping to off-island buyers. That means storage, insurance, and transporting firearms.
Customer traffic in and out
Security to prevent theft (strangers entering your place includes risk of a holdup)
Insurance to cover loss from fire or theft (Insurance companies may not be as lenient interpreting the ordinance if you aren't zoned for "firearm sales")
Neighbors complaining that they don't want a "gun dealer" where their kids live and play.
Your Dealer FFL would allow you to buy and sell guns. It might take extra effort to convince the local government officials you are not going to engage in actual firearms sales.
The ATF (at the moment) will only approve an FFL applicant if you state your intention is to actively engage in the business of dealing firearms. How they weigh FFL transfers only versus actual sales, I do not know.
If zoning is your only concern, you need to contact the zoning office and get specific guidance. For instance, you might be fine from a "gun sales" definition, but is there a school nearby?
I have a Class 03, which actually bars me from being a dealer. I have no direct experience with the other FFL types.