Please send your son to preschool. :)
Do not worry about academics. Your family will need to work on supporting your son's self-care skills (like dressing). Toothbrushing will still need adult support at least once a day. Let him 'brush' his teeth once a day, and you do it with him the rest of the time.
Preschool isn't necessarily about academic growth as much as it should provide a foundation for your son's social growth. Learning to care for himself, to move through the day with the group, to play within the group, to follow the teacher's directions... all of these come with the territory.
In the meantime, you can find toys that have zippers and buttons for him to practice on, because children need to work on manipulating those parts of their clothing. When you say that he can 'barely get dressed by himself', are you referring to fastening closures or actually getting the clothes themselves onto his body? If it's the fasteners, well, that's going to take some time. I encourage parents to use simple clothing at younger ages (pants that use elastic instead of relying on snaps and zippers, nix the overalls, too) . At four, your son should be getting his underpants, socks and shirt, pants, on by himself. He *should* be completely capable of this. I have a four year old son who will do a lot of "I can't"... we've learned to let him dress on his own in his room and that he doesn't sit down for breakfast until he's dressed. We had big tears the first week or so, but you know, now he does dress himself at least twice a day. If there's a physical reason he's not able to dress himself, talk to your pediatrician.
Many children don't like to wipe their own bottoms. My tactic with my preschoolers and with my son is to ask them to 'wipe two times', and I do a lot of supporting this. They need to know how much toilet paper they need (at least 4-5 squares, folded, not balled up) how to hold it in their hand to cover their hand, how to stop after they've wiped their bottom so that they don't trail the poop up their backsides. Some children are worried about getting the poop on their hands. What helps is to be consistent and low-key about it. (No, "eww, yuck, oh no, I've/you've got it on your hands".) Be present and supportive afterward too, because you want to make sure his hands are washed thoroughly and if he does get feces on his hands, he'll need you to turn on the water.
Focus on giving him lots of support for self-care, get him into preschool to learn the social piece of being in school, which will give him a considerable leg-up for kindergarten, and then give things some time. The preschool transition often finds parents wondering if they did the right thing, because our children tend to need us more. My son wanted me to 'do' more for him once he started preschool, and his teachers have been great at helping him to 'grow up' a little more.They will be practicing independent self-help/care skills at preschool, so they do become more needy at home. Set good boundaries around this. (For example, sometimes I'll be 'company' while my son is getting dressed, but I won't do it for him.) Being at preschool is work to adjust to, so be prepared. And know that this will be a really great first step. Likely, he's going to be more ready for the academics-- letter/number recognition, etc-- when he's older and in kindergarten.