Selling online is not uploading a catalogue
The usual expectation is that an online store adds sales without adding work. The reality is that it can add a great deal of work if it is built disconnected from the rest of the operation.
Every order that arrives through the web and has to be re-entered into your management system is a sale with a hidden cost. Multiplied by the volume you hoped to gain, the saving disappears.
Where the hidden manual work shows up
In three places, almost always. Stock: if the store does not know what is in the warehouse, someone checks by hand or you sell what you do not have. Prices: kept in two places, they will eventually diverge. Orders: if they do not reach your system, someone transcribes them.
None of the three is noticeable at five orders a week. All three become a problem at fifty.
What to integrate from day one
The viable minimum is that the order lands in the system you already work in, and that stock exists in one place only. That resolves most of the manual work even if everything else waits.
Payments and shipping are usually solved by existing integrations. What rarely comes solved out of the box is the bridge to your management system, because it depends on which one you use. That is where development effort belongs.
How to start small
You do not need the whole catalogue online. Start with the products that repeat most and generate the fewest questions: the ones a customer can choose without asking anything. Those sell themselves and perform best in a store.
Products that need advice can stay as enquiries, at least at first. Selling online does not mean everything sells unattended: it means whatever can resolve itself, does.
Do not start with the tool. Start with the friction and the outcome you want to change.