Here are a few suggestions for choosing a reasonable amount of magazines for your fellowship:
Figure out how many households regularly attend your fellowship. For starters, order enough so that each family can have one copy, or at least enough so that 10% of attendees can have one.
Keep in mind ministries within your church that might need extra. If you have a greeting ministry, provide them with extra copies for first-time visitors. Your local outreach team can distribute copies to the community, in waiting rooms or coffee shops, for example. Announce the arrival of the magazine to your fellowship and offer a taste of what is in the latest issue by showing a preview video.
A month or two after your magazines arrive, evaluate whether or not you need to increase or decrease future orders. Let us know in time to change the amount before the next issue ships out.