The goal is the whole game. Set it too high and a campaign that would have been fine looks like a failure. Set it too low and you have not validated anything. Here is a grounded way to pick.
Start from your real production minimum
Most made-to-order runs have a minimum that makes the economics work: the smallest batch your manufacturer will do, or the number of units where your per-item cost is sane. That number, converted to units or revenue, is your honest goal. It is the point where you can actually say yes to production.
Set the deadline to match your audience, not your patience
If you have an engaged list or following, a short window (7 to 14 days) creates urgency and most of the orders come in the first and last 48 hours anyway. If your audience is smaller or you are relying on it spreading, give it longer. The countdown does the nudging for you.
Use the cap to protect yourself on the upside
If there is a number above which you physically cannot deliver on time, set it as the max cap. The campaign will stop selling there automatically. Goal is your floor, cap is your ceiling, and Fundcap enforces both.
One more honest note: Fundcap does not bring you an audience. It gives the audience you already have a reason to commit. If you have no list, no following, and no email, a campaign cannot manufacture demand from nothing.