Motherhood is a huge adjustment, SAH or not. I would imagine that going from having a time consuming successful career to a SAHM of one is even harder.
For me, I get happiness from doing my best, which sounds really cheesy, but it's true. I do not iron my aprons so someone will see me in my apron and say "wow, your apron is so wrinkle free!" I do it for the satisfaction of doing it, and being busy, even if what I'm busy with isn't "important" if that makes sense. I use the apron example because obviously no one will ever compliment me on my nicely ironed apron especially because it is constantly filthy, but it applies to everything. Making bread, ironing the collars of my kids shirts, cleaning my house, etc. I don't enjoy any of these things as what they are, but I do enjoy keeping busy and I feel satisfied when I am done. I think a lot of this is important to being a homemaker (or a SAHM) because so much of what is done in the home isn't noticed, and isn't going to get much recognition, which is different from most jobs outside of the home. And a lot of what we do is gone within an hour, a lot of times less. Dinner? Gone in 20 minutes. The toys in the playroom? Back on the floor as soon as the babies get to it. Clean freshly folded laundry? Some of this usually lasts for a few days but there's always dirty laundry to replace it. A lot of this stuff would probably be noticed if it wasn't done, but some of it wouldn't be noticed for weeks.
1) are truly happy about their life (satisfied, fulfilled, etc)
I am very happy with my life. I wouldn't change anything about it. This has not always been true, I used to be fairly miserable and nothing has really changed about my situation, just my attitude and the way I go about life. I don't wish for help or a few minutes away from my kids anymore. I am not resentful anymore.
2) are properly stimulated, excited, interested, and not bored
I am certainly not bored! I'm excited about life, the future with my family, the baby I am growing, spending a long weekend with my kids, getting the grill out tomorrow, the movie I am watching with my kids tonight, the brownies on my counter.
3) are not feeling lonely or alone
I do sometimes feel lonely. My husband is deployed right now and communication is not great. I don't dwell on it though, I just write him a letter or an email when I am missing him and wish I could talk to him. It helps a lot. I did this before the Navy came into our lives, too, just a little note to leave for him when he got home. I also have a couple of good friends to sit and chat with from time to time. I haven't always had that, but it's nice when I do. I have a lovely neighbor with three daughters the same ages as my three youngest. We will grab an extra latte when we're out and bring it to the other, things like that. I also have my kids to keep me company. Mine are older than yours though, I believe, so I know it's different.
4) are feeling beautiful & sexy (not feeling like an ugly, unattractive woman passed their prime)
generally, yes, I feel this way. For me, it's important to wash my face and brush my teeth as soon as I am awake. Getting dressed in real clothes follows shortly, as does spending a minute on my hair and maybe a little mascara. I do my nails once a week or so, never anything but clear polish on my hands though because nothing looks worse than chipped nail polish. Showering is a challenge for me, I'll admit it. Sometimes I can get a quick shower while my kids are busy but I always hear them screaming or crying (it's in my head, apparently I'm crazy) while I'm in there. So generally I take a bath with my two youngest every other day. I wash my hair in the sink because I can't stand to wash my hair in the bath, I don't know why. I love a good shower but at this point it's just not in the cards for me so I don't stress about it. When my MIL comes to visit after the baby is born I can take a shower.
5) are feeling great about themselves in every aspect
I am hesitant to say this is true, I know there are things I'd like to change, but I am very happy about myself in general.
6) feeling accomplished, have goals and meaning
I feel accomplished. But I don't get a sense of accomplishment because of any huge things that I do. I feel accomplished when I learn to do something new, or when my kids do something amazing and I feel like I have contributed to it. I have goals, most of them are little things like dragging my dh's grill out of the garage and figuring out how to use his chimney starter and not burn anything. Some things are bigger, raising five loving responsible decent human beings is one of those. But it's hard to see stuff like that day to day, I'm going to have to wait about 20 years to see how that goes.