ScottP's list is a good one. With any piece of gear, always ask what benefits you're really getting if you go with a larger/heavier/pricier option over the lightest/cheapest/most basic model. For instance, since you're a side sleeper you might want an inflatable air mattress like that Big Agnes pad you looked at rather than a Ridgerest. It will be heavier, but better sleep may be worth the weight increase. Likewise, you may decide you prefer the bug protection and slightly easier setup of a tent over a tarp since you've not had much experience hiking yet, even though the lightest tent on my list weighs at least double the weight of the tarp ScottP has suggested. But what do you gain by carrying a 5 pound, 2-person tent instead of a 2 pound, one person tent? Nothing of value, just extra weight. Why carry an 80 liter pack if everything will fit into a 30 liter pack? The larger pack will be heavier, and the extra room isn't something you need; again, that's carrying extra weight for no gain. What does a 1 pound traditional pump filter offer that Aqua Mira or a 2 ounce Sawyer Squeeze filter doesn't - apart from complexity and extra weight?
As you've already discovered, your local outfitter and REI are both happy to weigh you down with heavy, cumbersome, unnecessary "necessary" gear. Think in terms of simplicity, lightness, and safety when you put your kit together, and you won't go wrong. Make every piece of gear EARN its way into your pack! Hiking's more fun when you're not imitating a pack mule.