Hi and welcome to HOD! I only have a second but can try to answer a few of your questions.
--In my state (GA), I see that, starting at age 6, the subjects "social studies" and "language arts" are required, among others. Do I need curriculum with these titles specifically or will general curriculum (i.e. HOD) cover those subjects? It seems like learning the alphabet, phonics/beginning reading, listening skills, etc. would cover "language arts". For "social studies", what would that include? Day-to-day teaching your children about the community and persons? Field trips to places such as fire stations?
We are in MO which requires similar subjects. HOD's history covers social studies just fine as they learn more than just history. Extracurricular activities and everyday teaching would count too.
--Also, in my state, it says that the homeschool day must be at least 4.5 hours long. It looks like the HOD curriculum doesn't take nearly that long, at least in the early years. So would other learning/activities/reading count toward that 4.5 hours or just "school/curriculum" time?
MO requires 1000 hours per year...which is roughly 6 hours a day. There are different ways to get hours in. If you compare our day to public school, they have an hour of math, but a lot of that time is passing out materials, answering questions, teaching the subject in multiple ways for many children, dealing with distractions, etc. So, you are still getting the same amount of math as them, just in less time. Because of that, most resources I've read say it's okay to round up to the nearest half hour. So if math takes 15 minutes, you can count that one session of math (or 30 minutes). Other people keep track of activities outside of curriculum and let that count. If you google search for how to count homeschool hours in your state, you'll probably get some good advice!
--I'd really like to start and finish with one curriculum if possible, for ease and continuity. I'm afraid something would get lost in the shuffle with changing curriculum. Does HOD cover everything from Pre-K to graduation from high school?
Carrie is currently finishing up the high school guides, so by the time your little ones are ready, high school will be ready too.

Though, don't be afraid to change if something doesn't work...better to have a period of shuffling and then a long stretch of things working, than to struggle with the wrong curriculum. (Of course, I'm a bit biased...I love HOD and hope to use it all the way through
--Is there any way to know/any resources that show students' scores or academic success with a curriculum? I'm in the medical field and have no previous experience with children so I just want to make sure that the curriculum I'm choosing will 1) Help them grow into people who will love and serve the Lord and 2) Ensure they've received a good, thorough education and life skills (beyond what is required by the state).
Not sure about this...but I do know from what I've researched and read, HOD covers all your bases and then some!!
--My 2 y.o. was born in November and so I'm not sure if it'd be best to start her in preschool when she's 3/almost 4 and then start her kindergarten year the following year when she's 4/almost 5? Our second child will be born in January, so I don't know if it'd be best to start preschool at age 3.5 and work on for one or two years and then start kindergarten at either 4.5 or 5.5?
My oldest son also has a November b-day. We just started Little Hands to Heaven (LHTH) when he was ready...which was in January after he turned 4. If you follow a traditional calendar, then you would just do half the guide in the spring and finish the rest the following fall. We school year-round, taking off whenever we want, so it doesn't matter when we start and finish guides.
Also, if you are excited to get started and she is ready earlier, you can start LHTH whenever you want. It is set up in such a way that you can go through the guide 2 times...once using younger resources and the next time using older. Or, we are currently using LHTH with our 5 year old for kinder--adding kinder math and phonics (we didn't do preschool really...just taught him through play).
All that to say, there are lots of options and you can just do whatever works for your family. There is no hurry. The next guide, Little Hearts for His Glory (LHFHG) works great for k or 1st. So long as your kids are in the age range for the guides, you're generally good to go.
--How do you know which Drawn Into The Heart of Reading level you need to use?
-Should you begin Drawn Into The Heart of Reading at age 6/1st grade? For the additional language arts choices, it starts at English 2, recommended for grades 2-3 so should that begin with age 7/2nd grade?
HOD does phonics first--in LHFHG and Beyond. Once your child is done with phonics, she will move to the Emerging readers books (in Beyond or Bigger). Once she completes the emerging readers set, she will start DITHOR 2/3 (in Bigger or Preparing).
Rod and Staff English 2 is used in Bigger. It is very advanced, so it would work for 2nd or 3rd--depending on when you get to Bigger. HOD does once a week grammar in Beyond in preparation for English 2 in Bigger.
Grades are pretty flexible in homeschooling. My son just turned 8 and if he were in public school he'd be in 2nd. But here, he's in 3rd grade math, English 2, middle of the emerging readers set, which I think puts him somewhere between 2nd and 3rd. We started Bigger in March, but I may stretch it out a little if he needs more time to work on his reading before starting Preparing (which has independent reading for the first time). The joy is that I can just go at his speed. We slow down subjects when he needs to work on a skill, then speed back up when he's ready. He's a math wiz, so we just keep pushing ahead in math, but he's not much into reading and really not a fan of writing, so we are taking our time with that. Don't be afraid to go at her speed and know that it's okay if one guide spans more than one grade (like Bigger for us will be part of 2nd and part of 3rd (as far as public school is concerned).
--Also, any other information or advice or resources would be greatly appreciated.
I would just add, enjoy these early days (not that I'm very far removed from them, lol). The early guides are sweet and gentle and a lot of fun...things will get deeper later, so enjoy the shorter days now!
Hope that helps some...and hope it all made sense. We all have colds here and I should probably be in bed, lol. God bless!!