First off, we advise to order when you will be online on FUT. As our delivery is usually within 6 hours (can be up to 24 if busy), we advise that you will be online ready to receive your coins. We suggest that you use the coins immediately, whether it is on your players, packs or anything else you would want to spend it on. As if you get a warning or coin wipe then at least you have used your coins and lost the minimal amount possible. This is just a safety precaution.
We recommend that you buy 100k or less every few days, ideally, to keep the risk down. But if you really want that Pogba, or that Ronaldo, and you've had no warnings, then buy the amount you want to buy, list up players equating to the amount you have bought, then use the coins immediately. This way if you get a warning or anything happens, you have got your marquee player.
Got coins left over after following our advice? Don't worry. Stock up on plenty of Team Fitness & All Injury + 4 cards. They will ALWAYS come in handy. Then if the worst happens, you have your team, plenty of fitness & injury cards and the minimal harm has been done!