Yeah you really got to mix well when topping off to get an accurate reading. That being said, since you used extract, you can reasonably calculate what your starting gravity should be based on how much extract you used and your total volume.
I don't have the space nor brew enough to keep bulk gains around so I just order the gains I need when it's time to brew. I'm usually just finding recipes online that I think some tasty.
With hops I usually order what I need unless a place like Yakima Valley is having a sale on a hop that...
Your dad liked his beer light, to be sure. I guess that all depends on how big of a can the malt was. I'd go light on the hops because so much sugar will dry it out and I'd think anything over a few IBUs will be quite bitter.
The chiller is an investment for sure. If there's even a possibility of you moving up to 5 gallons, I say go with the bigger one. Spend the money one time. But it's easy for me to spend money that isn't mine lol.
It's got to be a stratification thing. There is just no possible way that the pre-boil and post-boil gravity can be the same, unless you have almost no boil-off.
Could there have been stratification in the sample you pulled? So that the wort was actually more concentrated in your sample than throughout the whole volume of liquid?
What temp are you letting them carb at? If it was a little lower, 11 days may be a bit too early. If that's the case, you could just wait or move them to a warmer spot and give it another week.