Upgrading to BFV or BF at CSA

We have a honeymoon booked at CSA for september of this year. At this time we have a garden verandah booked, but after reading the boards and looking at photos I've decided I want to pay for an upgrade. When we booked the garden we got a $300 resort credit. I'm assuming that we could use that toward an upgrade once we are at the resort if there are BFV or BF rooms available, am I right? I was wondering a couple things though. For starters, what are the odds of an upgrade being available in September once we get there? I know it's a slower time but I don't want to risk it. Also, would it cost me less to upgrade now and lose the $300 resort credit than to wait and have the rates go up by the time September rolls around and then try to use my $300 toward the upgrade once we are there?

Also, which is closer to the beach bar, the BFV or BFs? I have a feeling we will be spending a lot of time there :)

Thanks!