You will need to have your own NEM wallet or address to store the XEM; multiple wallets if your prefer, but may be harder to manage. I would also recommend implementing multi-sig account to hold your XEM funds. Doing so you can have multiple NEM accounts manage that one multi-sig account for things like withdrawals.
Yes multi signature is a great improvement in security. Trezor for example too. The firmware update yesterday enabled NEM on the newest model (Model T) with many other coins. It always works like a charm and is a huge improvement too if someone just wants to use one device