1. You need to compute the cross-sectional area and and compute the current carrying capacity based on the area of the foil. This will give you the DC capacity.
2. For high frequency AC, if the foil thickness << penetration depth (skin effect) you should be OK. Else you should consider the thickness as the equivalent penetration depth. The current capacity will be accordingly reduced.
3. You need to decide the width, from the limited range of choices, based on the final current density.