Yes, if I was in a budget crunch and trying to keep SPS, I would dose 2 part daily by hand, run a GFO reactor and run carbon passively in a filter sock.
Regarding filter socks. There are two general ways that they are used. Most people use them for mechanical filtration on the drains from the main display tank into the sump. Those filter socks should be changed out and cleaned at the very least once per week, and preferably more often than that. Filter socks for mechanical filtration on drains usually have a plastic ring like
this.
People also use filter socks to hold media like activated carbon which is what I am suggesting. When used for media, you don't put the sock on the drain, you just put carbon in the sock and close it, then put it in a high flow area of the sump where water will flow around it and through it to some extent. You don't need to clean the filter sock as often as in the first example because you aren't flowing as much water through the sock and aren't trying to use the sock as mechanical filtration. Socks used for media should not have a plastic ring, but instead should have a draw string to close them like
this.
I do not like the BRS dual reactor, even though it is a good value, because carbon and GFO have different optimal flow rates, but that is better than running carbon in a filter sock. My order of preference:
1) 2 independent reactors, 1 for carbon, 1 for GFO
2) a Dual reactor running both carbon and GFO
3) a reactor for GFO, and carbon in a filter sock in the sump
Regarding the reef builder on your shopping list: I've never used a powdered alk & cal supplement like that but I know someone that swears by the similar Tropic Marin Bio-Calcium product. I stick with 2 part liquid supplements like Kent Tech CB, ESV B Ionic and Randy's 2 part recipe.