I like the advice you've received so far! Stagger starting your dc will help you get your oldest in a rhythm first, then your next child, then your last. For your oldest child doing PHFHG, you will want to help her begin to learn to use the PHFHG guide as a student planner, reading the directions for her "I" independent boxes herself, and initialing the corner of each box as she finishes it. I would have a certain routine order for her to do the boxes in, as this will help her settle into a good routine from the start. Giving her a type written or handwritten list of the order of this routine will really help keep moving her along. It also cuts down on the constant question "What do I do next, mom?".

Training her to read through an "I" box's directions carefully, get her supplies out, think through the order she will do things in, and then read through the box's directions step by step as she does one step at a time will help her learn to be a good worker. At the end of finishing an "I" independent box, I have my dc read through the box one more time to be sure they did it all. This would be a great way to begin training your oldest dd first in PHFHG. I'd say 2 weeks would be more than enough training for this.
While you are training your oldest to do PHFHG, you can have your 8 yo practice having a playtime with each of your younger dc. We have found 30-45 minutes to be a good time frame for playtimes. Your 8 yo can have a playtime with your almost 6 yo, and then have a playtime with your 3 yo. Likewise, your 6 yo can practice having a 30 minute or so playtime with your 3 yo. These are important training times for them, as they will help you out immensely in the flow of the school day.

Having a planned snack time and a few other independent things can help too - i.e. an independent playtime for 3 yo in a safe childproof area, possibly an educational video and/or an educational game on the computer, maybe have 8 yo have a time to read a few books to the 3 yo, maybe a book on tape time for some of them, etc. Fostering some good independent playtime and activities really helps out in the day to day of homeschooling.
Next, you can train your Beyond child. This should not take long. I'd say a week or so. Finally, you can start LHFHG with your next child, maybe starting half-speed.

Meanwhile, during this time, your oldest 11 yo can begin taking a playtime with each younger sibling as well, or with a pairing of dc if that's easier (i.e. 3 yo and 6 yo while you work with 8 yo). Your 11 yo will have the most work to complete in a day, so the playtime can be less if needed - whatever is most helpful is what you can choose.

You could have your 11 yo teach LHTH to the 3 yo eventually, at least part of the time, if you wanted too - but that's maybe further down the road.
A rotation of times for me when I will work with each child REALLY helped me get into a good routine and know who I was focusing on teaching when.

Here's a copy of our last schedule for RevtoRev, PHFHG, and LHFHG half-speed, in case this helps make it more visually understandable what I'm trying to explain about teacher blocks...
Or, if you prefer, this is pretty much the same above schedule after I typed it as more of a routine than a "schedule" later in the year...
These are my best tips for happy homeschooling with multiple dc! Having a routine, having teacher blocks of time, and having the olders take turns playing with the youngers - works great! Makes it so much easier to homeschool without the stress. HOD really is just an open and go curriculum - pretty much no planning or prep to teach each day. So, if you just put a little time into stagger starting, doing some training of independent things other dc can do, and set up a routine order of teaching blocks, you will be set all year for smooth sailing! HTH!
In Christ,
Julie