Std MX brakes are ok for a novice but I wouldn't be keeping them on for any serious work! We were playing with some twin brake set ups in WSC but jury is still out on them, were also using 300/310 and 320 front rotors. If your wanting decent brakes then Moto Master has some entry level units for conversions or you can go straight to their top competition models.
Alloys are starting to be used more but ex road bike wheels can be a bit dodgy. Also alloys and carbons have a tendency to break. Alpina's are tubeless but expensive, most are running them or a top billet/spoke wheel. A few in Europe were trying the carbons, but again reliability is still an issue.
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