Good bibs - or even "just" cycling shorts - can make a world of difference. I bought an entry level Nalini short, and a few weeks later, a basic Castelli (Presta model) bib, and it's a huge difference to riding with non-cycling pants. They're shaped not to interfere with your motions while at the same time padding where it's necessary - and you'll feel the sweat much less.

Jerseys are not a requirement per se, but they're highly useful. First, most of them come with rear pockets for storage - I can cram my mini-pump, tube, levers and food in there. Second, they're usually made from sweat-wicking and more form-fitting material than regular tees - again, comfort is the key word here.

Equipment - as was said, a pump. Lezyne's Pressure Drive model was my choice, and pumped my tires to 100psi without too much of a problem (it's never easy with a mini-pump), comes with a neat flexible tube to prevent breaking the valve (and allows better leverage) that stows inside the pump, as well as a mounting-bracket that mounts to your bottle-bosses - fits neatly next to my bottle-holders without sticking out and interfering with my movements. A mini-tool is also highly recommended.

As for tweaks: My sure it absolutely fits you. Obviously as you get used to the bike, you might want to make some changes - but make sure you're comfortable from the get-go. I found a comfortable fit, and then as my strength and goals changed, I turned more and more aggressive with the setup - dropped a spacer every few weeks, and adjusted my saddle to match. It's all very individual and maybe the Trek store could help - mine did when I bought a 1.2 model. I, for example, prefer a very steep seat angle - I'm at the end of my saddle-rails as it is - and the fitter at the store figured it out even before I thought about it.