As for topping up, every winemaker should try finding different vessels for secondary aging. When we can't fill a carboy, we will use gallon jugs instead. We also have some half gallon jugs, but those large wine bottles are the same size. We use marbles or glass spheres that are used for decorating glass jars, which you can find in craft stores or the Dollar Store. Glass is inert, so it is safe to use. Just put them into a meta soak for a few minutes and then add them to the jug. We've been using them for many years with good success.
There are some other principles to keep in mind too. You should always know the PH of your wine because this dictates how much free SO2 a wine needs to avoid oxidation. Using .8 mol as a target, a wine with a PH of 3.3 needs 30 PPM---while a PH of 3.8 needs 80 PPM.
Additionally, keep the fluid level up in the airlock, don't remove the airlock repeatedly, don't thief the wine lowering the level too far, and don't manually degass unless you are doing kit wines.
