Homemade LED flashlight
My idea is to use boost converter IC to step up voltage and use shunt in series to sense current through the LED and connect it to feedback pin of the converter


I did something similar about 10 years ago, used a LTC3780 buck-boost DC-DC to make a constant current LED driver by adding a current sense amp in the feedback loop. However these days there are LED driver chips that can do all the current sensing stuff without requiring extra circuitry, so that would be a simpler and much better choice.

Now for the bad news...

Very high power flashlights usually don't have useful battery life unless they weigh a ton.

For a 30W LED, a buck converter would be more suitable and more efficient than a boost converter.

Looks like you want to use an "extreme" LED with very high power though... 30 watts...

How are you going to fit the cooling fan for the LED heatsink inside the flashlight?

The most important thing in a flashlight is the optics. Power is a distant second. A high power LED with wide flood beam optics will make the ground at your feet very bright, and you won't see anything in the distance. A less powerful LED with good optics will have a good throw and be much more pleasant to use.


  I can't seem to find any CC/CV charger IC that would be suitable for 2S cells and THT soldering


Seriously, if you're asking that question, I don't mean to be rude, but you sound like you should have the firemen on quick dial if you mess with lithium batteries.

Lithium cells need to be charged to a quite accurate voltage, and if the battery pack has several in series they have to be balanced. This plus adequate protection requires a complicated circuit, and the schematic in the question won't do that. If you want a readily available and safe lithium battery, either use the battery from your power drill and its charger, or use protected 18650 cells.