TrainHead,
First, let me say [#welcome].
Second, command control, system itself, you will want one of the top two brands, NCE or Digitrax. Both have very good starter sets that are expandable as your layout progresses. Motor control decoders, with sound most like TCS and ESU. Basic motor only add in NCE, and Digitrax. Tsunami’s (Soundtraxx) have very good steam sound, but lack some of the finer motor control. QSI also is pretty decent for sound decoders, but falls behind the TCS and ESU in motor control.
One caution- unless you will only buy MTH products, only run MTH locomotives, and never buy anything made by any other brand for locomotives, do not buy MTH’s DCS system. More on that below…
Track brands, ME (Micro Engineering), Peco, Atlas and Walthers/Shinohara. Most prefer flex track, where the roadbed is seperate, as it allows more flexability in track plan. You are not restricted to only what sectional pieces are made by a certain manufacturer. ME flex is more detailed, but is stiffer than Atlas flex. The others fall in between.
Highest detailed motive power, falls to Atlas Master series, Kato, Intermountain, Bowser Executive line, Athearn Genisis line, BroadwayLimitedImports (BLI), and possibly a few others are the favorites. Bachmann Spectrum, and Walthers Proto are also quite detailed. Bachmann Standard line is less detailed, as is Atlas Trainman line, Walthers Trainline, Athearn RTR (ReadyToRun). But, they are a little cheaper in cost.
With you being former O gauge, I will caution, though MTH maybe a known brand for you, they leave something to be desired in HO Scale. Their locomotives do have good detailing, but their DCS system, and locomotives, are designed to run at a higher voltage than any other brand in HO scale. This means you can not get full control capability unless you buy their DCS system, as MTH has not become fully NMRA