Welcome! Your idea of starting with short trips and gradually adding time/distance as you gain experience is a good one.

For starters, read the articles listed on the home page of this site, left-hand column. Many of them are about gear selection. Pay special attention to the advice to get your backpack last! There are also several gear lists there.

I'd also recommend Andrew Skurka's book.

A great place to compare various gear designs is Mark Verber's almost encyclopedic website. You can also check out the comprehensive gear reviews on BackpackGearTest.org.

When starting out, renting or borrowing the major gear items, or buying them used, is an excellent idea. A lot of clothing items are probably in your closet. I'm sure that a number of your car camping items are usable. You really need to gain some experience before investing $$$ in a lot of new gear. Otherwise you'll find yourself replacing over half of that expensive new gear before the first year is out. .

Many of us have long since given up boots in favor of lightweight trail runners. I made the switch 4 years ago and never regretted it. The trail runners are far more comfortable and also more supportive. In fact, my hiking boots have stayed in my closet unworn ever since. I have gone as far as putting them in a box intended for Goodwill; as soon as the box is full, the boots will be gone for good.

Here are some low-budget oriented gear lists, just to show what can be done for a relatively small amount of money:

Cheap Ultralight Gear List

Mark Henley's Ultralight Gear List

"Sgt. Rock's" Dirtbagging and Deal Shopping

There are also low-budget options listed on Mark Verber's site linked to above.

This should give you enough research sources to keep you busy for a while!