Basic speaker upgrade advice wanted. Kind of time sensitive...

Backstory:
I've had stereo systems in other vehicles that I've installed myself consisting of diamond audio components/technique amps/fosgate subs/capacitors and the works. I've loved them and I've learned that a stereo is only as good as it's weakest component (usually the HU). I would like to keep the stock HU due to theft prevention and warranty which I have for another 50k miles. So, I'm looking to upgrade the truck speakers. I heard mr marv was the man to talk to but I'm thinking about jumping on a black friday deal this weekend. I am not looking to nor can I afford a system at this point. The stock stereo is almost good enough for where I am at in life now but sometimes I want a little louder volume and a bit more bass. My goal would be to put in a pair of 6*9's up front and upgrade the rear. That should accomplish my goals. 2010 Access Cab, non-JBL.

Questions:
What sizes have you run with success?

Does the JBL system come with upgraded speakers that I could use? Are they much improvement?

I don't have experience with 2-ways or 3-ways. Anyone tell me (possibly from experience) what would be best to add to a STOCK system? I know it won't be as good as a component set but that's not what I want.

What have you installed (brand/model) with success? Thoughts on improvement and shortcomings?

Did you keep the tweeter hooked up or DC it?

Wattage range you have used with success? I know under powering a good speaker will negate the improvement but I do believe that a speaker with a better cone/magnet should improve the stock system by as much as I need it to.

Best buy has a deal on Pioneers right now and its walking distance from my house. I went browsing this afternoon while at work and that got the ball rolling on the idea. I will get a kit from taco tunes for the install.

Thank you in advance and happy holidays. I hope you had a wonderful and safe time with family and friends.

Evan