A couple questions about my new cat

While almost everything is going well, there are a few things Im a tad concerned about and wonder if it will get better. Im taking turns with the cats on who gets to roam the house and who stays penned up in the computer room. It seems to be going ok this way. Last night Jayce stayed in it overnight and was in the same place I left him He really seems to be very very timid. Hes still scared, so we're going slow on learning the rest of the house, but hes jumpy and freaks out about a lot of little things. He wasnt quite this way at the shelter, so maybe Im just expecting too much too soon?
I just dont want my 3 year old scaring him. Shes very respectful and gentle and treats them well, but her antics (typical of a happy 3 year old) will freak him out. Is this something that will take time or is it likely to be part of his personality? I just dont want him to be scared of her, as thats not fair to either one of them. I did ask at the shelter if they thought it would be an ok fit and 2 of the workers there said they thought he would be fine.

The second problem, is that all the cats seem to stalk the crack under the door where they can see each other and reach their paws under. Its about 2 inches of space which I thought would be good to help them smell each other out and all. But they swipe paws at each other and there has been a little bit of hissing. Is that normal too? Should I keep them seperated like this for about a week? What indicators tell you when its an ok to start meeting face to face? Ive done the vanilla thing and will keep it up for a while, and also have their food bowls on opposite sides of the door.

Keep it up, you're doing fine. Hissing under the door is normal. The real signs of agression include growling and fierce "attacking" - claws out, trying to fight with the new cat. They should "meet" like that for a week or more. Take it slow, it will go better.

Just for comparison; when I introduced my second cat, I waited a full week to leave them alone unsupervised, and they had never even hissed at each other. It lets the resident cats get used to the idea of a new comer. Keep using the tips you read on this site.

I'm cat sitting, and waited a full week to leave them alone together. Its two weeks later, and they still hiss sometimes, but its just to let the wild and playful kitten know she they don't want to play.

(The new kitten's idea of fun is to make the older cats run and then chase them, they don't like that much, but it gives them much needed exercise, the lazy lumps)

Swiping under the door is more of a play thing than an attack. This is good. Hissing is normal and should take a while to ease off. They are deciding who is top cat.

I would give your three year old a feather wand and allow her to play with the new kitty. An old sweaty shirt of hers unwashed under his food dish will asociate her scent with good things.

Make sure you establish with her that if the kitty goes under something to hide it must be left alone until it decides to come out. This will allow the kitty to decompress and become more confident in it's new home.

It sounds like things are going well and your new addition will soon feel right at home.

BTW I just wanted to thank you guys for the responses I got too busy to reply earlier.. didnt want this to slip by without a thank you