A great question. And, with wetsuits as with other garments, one size does not fit all. And, the last thing you want is a wetsuit that allows water to simply flow freely through the suit because it is too loose, or a suit that is so tight that it impairs circulation.
You question is not - at this point - an issue of ordering a custom made suit. You just want to be sure that you have reasonable exposure protection for the upcoming dive. So, where are you going to be diving? A loose fitting suit in warm water will provide protection against contact with critters / fire coral, etc. and, even though it may not be thermally functional, in warm water that won't matter and a looser fitting suit will be fine.
If you are diving in cold water, you want a suit that hugs your body, and doesn't allow cold water to continue to flow through freely, and there are some options. Whether you go with a one piece or two piece, you want to be sure the suit fits around your hips. If that also means that either the one piece, or one or both pieces of the two piece (farmer john and shorty) are a bit loose on the top, one option is to add a vest - that fits your torso well - underneath the full, or two piece, suit. The good news about two-piece configuration is that you have some sizing flexibility. You may end up with a larger size for the farmer john portion, and a smaller size for the shorty portion - I have seen that be the case with a number of female divers, and with adjustment of the sizes of each unit, they are able to come out with a fully functional suit.
Now, as for the length of the extremities - a suit that fits snugly (but comfortably) around the ankles and wrist, even if it bunches a bit along the length of the arm or leg, is preferable to one that is too short, or way too tight, or way too loose.