Since these blinds will be mounted inside the frame, the attachments will probably be from the top of the frame. Toggle bolts would normally be my first choice but they need a large hole and about an inch of "free" space after passing through the 1/2" frame. If you have this space, go with toggle bolts.
If you're a handy person, a better ...
That anxiety will always live with you... it's part of mixing DIY "stab in the dark" with techie OCD. (I know.)
Most important with a window frame is making sure that
you have a generous drip edge above it,
water can flow through/over and not sit or puddle on any horizontal surfaces
you seal off all gaps and cracks that might lead to water running ...