I've been reading "Just Ride," by Grant Petersen who is the founder of Rivendell Bicycle Works. He gives good practical advice and doesn't think much of fancy gear and clothing. I agree.
The wicking, breatable, wind and water resistant clothing that works for hiking will work on bikes too. I do like padded shorts and I wear the baggy mountain bike style that has a padded liner. Bike tops come with drop tails and longer sleeves which may help. But there's no need to run out and buy a whole new wardrobe.
Shock absorber seat posts suck. They remind me of shock absorbing trekking poles, robbing power and lending a feeling of unpredictability. Get a good relatively firm seat and put the padding in your pants. Max Dilthey taught me that and he is 100% correct. Learn to ride properly, using your legs and body english to handle the bumps. Just paying attention goes a long way.
I like lights for safety. Get a comfortable helmet and wear it. Good tires help.
Like UL hiking, keep the toys and gadgets under control. The weight counts.