It doesn’t sound like you have a shifter as a Rotax 125 is used either for TaG (Touch and Go which means it has an onboard electric starter) or the Rotax specific series (Rotax Max). Any questions specific to the motor would be best posted in the “TaG” or “Rotax Max” forums. I used a Rotax in TaG several years ago and it was a solid engine package with longer rebuild intervals when compared to its competition.
If you are looking to run road racing (larger, higher speed tracks that are typically used for full sized cars) then the front brakes make be allowed; however, if you are planning to do sprint racing (typical sprint tracks will be around 3/4 miles or less in length) the front brakes will likely need to be disconnected. To confirm this, find the rules for the track/series you’ll be running and under the “Brakes” section it will clarify this. For what its worth, in sprint racing, I think most people prefer rear only brakes (except for shifters) for TaG/Rotax so if you disconnect them it will be one less headache/cost to deal with.