Cool! You could try building up your expression step by step, saving the cumulative expression in an instance variable (like seq in the example below):

| seqFaders seq eva rotation |

rotation := EventVariable new initialValue: 0.

eva := EventVariable new size: 8.

seqFaders := (1 to: 8) collect: [:i| !Interval suffix: i].

seq := (!Rotate switchedOn

true: (rotation <+ ((rotation + 1) mod: 8))

false: (nil)).

seq := (0 to: 7) inject: seq into: [ :expr :i | expr, ((eva @< i) <+ (((i + rotation) mod: 8) of: seqFaders))].

seq := (seq, (eva @< ((1 bpm: !BPM) countTriggersMod: 8))).

seq nn + !LogFreq nn