I'll chime in with the "four is too early to be writing letters" stage. I also recognize myself as too overbearing; it has been something I have worked hard on. But never fear: my poor daughter (my oldest; I was learning moderation) practically had to force me to teach her to read - I only worked with her when she asked the letter sounds and words - and she was reading at four. (I let her teach her brother, and they are both teaching my three year old now,

.) I had to consciously pull myself back.
If you want to work on some fun alphabet games, you can have them draw letters in sand or cake icing, shape them from clay, etc. My five year old still writes some of his letters backwards - but he was reading in last week's children's program at church and everyone was stunned when he covered big words like "sacrament", etc. I remember reading somewhere that children that age literally don't have the right muscle structure to be writing, and that forcing them to do it over and over like in a school situation can cause them physical problems, in addition to behavioral/educational.
As for "aptitude" for homeschooling - I struggle a lot with this. In all honesty, I am not sure that I have - or, rather, had - the right "leaning" towards being a mom. When I was a teen, I swore I would never had kids; I just didn't grow up in a great situation. Now I have four kids. I am by no means a perfect mom, but I have made a lot of changes. Nor am I a perfect homeschooling mom - before HSing, I was very excitedly waiting for my DD to turn four and GO TO SCHOOL and give me a break, I am ashamed to say. My point is that if something is important to us, we work hard to make the changes we need to make in order to achieve it. We won't do it immediately or perfectly, but generally the desire to homeschool stems from genuine love and concern for a child. If you want bad enough to change the things that YOU see in YOU as inhibiting HSing, you will. If you don't, you won't.
In the meantime, I can't imagine too many kids that would prefer to be stuck sitting in a classroom silently all day instead of exploring learning. <shrug> Any "problems" you see that are not age-related are just going to manifest themselves more strongly in a classroom.