If you're running a sump and skimmer on a 29 gallon tank, you will probably only need circulation in the tank, aka, power head or 2.
Circulation will be super important to keep the tank healthy and for the sump to be effective. Rio makes a wide range of submersible power heads that work well for nano tanks (anything under 30 gallons is considered nano).
You'll want to keep track of evaporation levels, and also spg/salinity so you know whether to add freshwater or saltwater at any given time. When water evaporates salt does not... so unless removing more water at the time, freshwater has to be used. If doing water changes everytime to deal with evaporation, you may need to lower the spg/salinity of the water going into the tank to avoid a spike.
If you're really worried about needing more filtration, a canister is probably the best way to go, but it won't offer the circulation, so power head will still need to be added. Eheim makes the best, but they are also expensive, and never go on sale. They are a German company and know they have the best out there, so they never allow sales or discounts on their products. If you want to save some money, the next best filter is still the Cascade, and even though not designed specifically for saltwater, they seem to stand up well for a very long time (7 - 10 yrs if properly maintained and cared for). Next down from Cascade is probably the Rena line of canisters... although I notice they seem to require much more maintenance than Cascade.