HI I am new to pro photography I never used SLR before
But with a
brief research on Google. Now i am thinking about buying Canon Rebel XTi 10.01 MP, with Canon EF 28-105/3.5-4.5 USM lens.
It behooves you to do more than brief research before buying your system. It took me months of study before making a decision, YMMV. You should also go into the stores and try to hold your choices and see if the controls feel intuitive, etc. Ideally, you want to make the right decision from the outset.
My main purpose is to take photos of babies(1 year old) , both indoor and outdoor. Pls tell me if i should use a
cheaper or more expensive len .
Of course i try to use as little as equipment but you think i really should buy lighting equipment, pls let me know.
At some point an external flash comes in quite handy. But as for lenses, most feel that that's where your money should "really" be spent. A lens with a large aperture, ie a "fast" lens, will allow you to take better pictures in low light without a flash, and of moving subjects, like children. (Of course, a large part of that is technique, also.) These can be quite expensive.
A "kit lens" will get you started and learning, but at some point you'll probably want a faster lens. Question is if it makes more sense to just get that in the first place. (Most probably get the kits.)
Lenses come in differing focal lengths so if you're only going to get one, it's good if it covers a good range. Most people wind up getting a few for different purposes. Also be aware that entry level Canon bodies do not have Image Stabilization in the camera body, so you should consider buying image stabilized lenses. These cost more than non IS lenses.
Generally how long should i expect to learn to be quite good at it?
This is the burning question, LOL. It depends how much time you put into it but I agree that anywhere from six to eighteen months should get you to a pretty good place if you continue to study and practice a lot. Of course, as mentioned before, some people keep it in auto, don't study at all, and are happy with that. It depends what you want to get out of it and what you want your pictures to look like two years from now.