Honestly it is probably early for a tranny flush and coolant flush, but it is better to do it too early than too late. I'm not about to tell you not to be proactive in the maintenance of your truck.

I wouldn't worry about brake fluid flush. Probably address that on your 2nd set of brakes, or your 1st set depending on how long they last. I would say around 100K.

As for the plugs, I have to be honest, on my 2004, I changed them at 115k, and they didn't look bad at all. I followed the TSB and broke 5/8 though. So its up to you. Honestly paying 450 + 25 x 8 plugs at 100k would be cheaper than paying 450 every 30k.

But hey, its all a gamble anyway. You could do them at 100k and they would come out fine, or mabye at 60k every one will break. Who knows.