I think you will find a huge difference between round dance and ballroom. On the surface they may seem very similar because round dance uses a lot of ballroom terms, but when you start looking at details, you will discover there are more things that are different, than there are things that are the same. Round dance is advertised as cued ballroom dancing, but that is not the case.
I'm not sure that knowing round dance will help you much with ballroom. It will be more like unlearning what you thought you knew and relearning it. Here is a list of only the major differences.
Round dance stresses learning the foot pattern for many patterns. Dance technique is usually not taught. The characteristics of what makes one dance different from another is not taught. Lead and follow is not taught. Essentially what you get are step patterns for many steps.
Ballroom stresses learning the techniques required to execute just a few patterns. Quantity of patterns is not important but how you do those patterns is. Once you learn the basic techniques, adding patterns is easy.
For round dance, patterns are usually cued in three step increments, but individual steps may be cued. Alignments and ending positions are cued, amount of rotation is cued, syncopations are cued. None of this happens in ballroom and much of the stuff that is cued in round dance would be considered incorrect in ballroom.
You get to enjoy the music much more in ballroom because you can actually hear it.
Change of footwork (syncopations) in round dance is done by the lady. In ballroom it is always done by the man.
Round dance execution of many of the standard dance patterns has been modified for round dance purposes, and some are actually completely different but have the same name.
In round dance, not everyone can dance all the time because everyone is supposed to be doing the same thing, and if you don't know the particular dance/song being cued you get to sit out. Or if it is a phase 2 dance and you are bored with that stuff you can sit out also. Most of the choreography requires that you have a training session on that particular song because most do not use only the standard steps, but they always seem to "invent" something for that particular song, None of this happens in ballroom. You can do every dance if you want, just do whatever steps you know.
You also don't need a cuer, cue sheet, and particular song to go with that cue sheet. For ballroom all you need is a danceable song.
Round dance two step exists only in round dance. It is not a ballroom dance, nor is it the same as country western two step. Slow two step also does not exist in ballroom, but it is somewhat similar to country western night club two step, except done at half speed. Most of the steps you learn in waltz phase 2 do not exist in ballroom, and nothing starts facing the wall.
Timing for several of the round dances are different in ballroom. Round dance cha cha 123&4, ballroom cha cha 234&1. Round dance rumba breaks on 1. There are three different rumba timings used in ballroom, one for International, and two for American, and they are all different from round dance. Round dance jive 12 3&4 5&6. International jive or American swing 1a2 3a4 5 6. Round dance mambo breaks on 1. American and International break on 2.
I can list lots of other differences, but I think maybe you should be getting the message by now. If you get started with ballroom, you will discover that it is a lot more fun than round dancing.