Also, how much time do you find yourself spending on program overhead (preparing receipts, meetups/mentoring/trips/presentations/etc)?
If you don't have enough money to pour in up front, cash flow will drive you crazy. Put together a six-month budget, even if it's loose. Put every expense you can think of in it. Reimbursements can only happen once a month and you absolutely need to plan things out to get the most out of the funding.
As for time on program overhead, minimum probably 2 days a month. Much more if you want to be more involved with the community. You are not forced to do much more than the reimbursement process and finding some ways to give back to the Chile. You could go to meetups and such 3-4 days a week if you wanted, a lot going on.