-Be sure about the fee you may incur topping up USD(I’m not sure)
-Do not exchange the money during the weekend
-If you are not a Premium user, after £5000, there will be a 2% fee: in your case I think it is better to buy the premium subscription.
-Check your annual limit and do not exceed it. If you need to exceed it, talk to the customer service first.
-I’m topping up has no cost, I suggest to start with a small sum of money.
-Be aware that a large sum of money may temporarily block your account for security reason. Talk to the customer service before topping up.
I’d say that’s all…but maybe someone else has some other suggestions.