Go to
the home page of this website. There are many excellent articles listed in the left column. Some of the brands are a bit out of date (for instance, Mountainsmith no longer makes light packs), but the general information is still valid. In addition to providing excellent information on a complete gear list, the "27-lb. 7-day gear list" enabled me to cut my total pack weight for an 8-day trip by 20 lbs. without sacrificing any comfort or safety.
You'll find lots of answers to your questions by searching on this forum. When you search, be sure to change the time parameters from the default time of one week! Be sure to check the "How to Search" thread which is a "sticky" at the top of the General Discussion forum.
Try not to let the standard outdoor stores like EMS and REI sell you bombproof heavy stuff (which is where they make their money). You really don't need a 6-lb. pack, 7-lb. tent or 5-lb. sleeping bag. However, you don't want to go to really ultralight stuff either, at least not until you've had lots more backpacking experience. The lists on the home page here are a good happy medium, with a base weight (everything except food, fuel and water) of about 15 lbs., give or take 2-3 lbs.
It's a good idea to buy your pack after you have acquired your other gear, and take that other gear (plus the equivalent in weight/volume of a week's food supply) to the store with you. Too big a pack, and you'll have trouble adjusting the load and be tempted to put more stuff in than you need. A too big pack will probably also be heavier than you need. Too small a pack, and you'll have to tie stuff on the outside, throwing the load out of balance and exposing your stuff to getting caught on brush, rocks, etc. But do go in and try on lots of different packs, even those bomber heavy ones, with a full load, so you learn how a well-fitted pack feels and how to adjust it. That way, if you have to order a pack off the Internet as most of us have done, you'll be able to tell if it's the pack for you while you can still send it back.
Check out the Beginner's section, too. Of course you have acquired plenty of skills from your extensive dayhiking, but since the Beginner's section is geared to beginning backpackers, many of whom have dayhiking experience, you should be able to find much useful info.
I strongly recommend starting with overnights in the back yard (yours or a borrowed one)--the safest way to become familiar with your new gear, especially in inclement weather. Your first wilderness campsite, in the dark and pouring rain, is not a great place to be trying to consult tent-pitching instructions by headlamp! Then take a few overnight trips, not too far from your car (just in case a midnight bailout is needed), before going out longer trips. Pick inclement weather for some of these short trips. It's really hard to force yourself to start out in it (it certainly is for me!), but that's how you learn to cope with those conditions safely.
Oh, and the compression layers? I think they would tend to restrict circulation, which you don't want. I like my clothing loose. You do need to be able to be able to get a base layer on under your shirt and pants, and insulating layer(s) under your rain gear. I'm a fan of thin, light layers. I wear the same clothing year around (although I don't backpack in winter), but use more insulating layers in colder weather. Your Mileage May Vary (common saying around here).
Welcome to the world of backpacking, and may you love it as much as I (and the rest of the folks on this forum) do!