The term “first advance” refers to money that you will receive right now. A reserve facility is a set amount of money that you can borrow from the lender in the future.
As an initial advance, it’s ideal to just release enough money to cover any expenses you expect to have in the near future. Any funds you anticipate needing in the medium to long term should be put into a reserve account.
This is because you will only pay interest on the money you advance; money in a reserve facility does not earn interest.
As a result, you’ll pay less interest, potentially saving you and your estate hundreds of pounds.