These questions are great questions that can garner a lot of opinions that are free and worth what you pay for them to help *your* game.
You really should work with a professional that can assess your swing. There is the quote from Arnold Palmer - own your own swing. 2 degrees up may be the best for you. Moving to stock/zero lie may force you to adjust your swing to compensate to the club, instead of the club adjusting to you.
The end assessment may be your current set is right for you, can have a small adjustment, or, you will be best served by a fitting to obtain a club that complements and not competes with your natural swing.

I may have sent a partial response by accident. So here goes the full response.

The drooping of the shaft you refer to is called the toe down affect. Even tour pros have this with xtra stiff flex. When you get fit for irons, the lie angle for your specs will reflect this. Lie angle is not determined on a static basis. If you go to a Titleist fitter with a Trackman, the Trackman will show how the bottom of the club is impacting the turf to confirm what lie angle you need.

Regarding lie angle, you could have a perfect swing but still need upright or flat lie angle depending on length of arms or other physical attributes. If your club head path is too steep coming down then that could cause a need for upright lie angle. You should get some lessons and understand what mechanical flaws you have. A golf teacher can tell you this and whether you should work on your mechanics before buying new clubs.

Like yourself, we are Titleist loyalists. Have you spoken to your fitter about this? That would be my recommendation. He is the professional that can answer this. With respect.

This is one for your Titleist fitter. That's what they are there for.

A lot goes into what lie angle you need. I've heard many say that better ball strikers play flatter lie angles. I think this comes from analyzing tour pro and top amateur swings. Remember that these players work on their swing, fitness, and mobility daily. Most of us who have jobs other than golf may never be able to consistently reproduce the impact positions of the pros obtain to shallow out. I would suggest a good fitting and go with their recommendations. Definitely work on your swing and if you need to change lie angle in the future your divot pattern will let you know.

Where are you contacting the ball? Lie angle directly effects this, whether it be middle, heel, toe etc

A good fitter will be able to determine what is best. Take the time to chose a fitter that has a lot of experience and understands the swing.