I would like to know more about RAW, most of the time I just drag my Jpegs into Lightroom and it seems good enough, what is benefits I can gain going to RAW?
RAW is exactly that, the raw data directly from your cameras sensor. To create your jpeg, your camera takes that same raw data and processes it with its own software referring to either the default settings or those you have chosen for it. In doing so, it throws away information it considers unnecessary to produce the final image; this missing information is very useful.
By saving your images in RAW, since the image is untouched, you have ultimate control and can choose in much finer detail how you would like your image to be processed using software such as Lightroom. The dynamic range you have at your disposal is much greater, allowing you to lift the shadows and bring back the highlights to a certain extent, should you under or overexpose the image (this of course, has its limits). You have fine control of the colour temperature or white balance in the image, it is not fixed as it is with a jpeg file. You have finer control over noise reduction and sharpness, specific controls on how colours are displayed.
Most importantly, since you are using Lightroom, is that you get the full benefit of it. Lightroom works best when it has the RAW file, with the jpeg much of the data is missing and Lightroom is hamstrung by what it has been given to work with. I know you're not saying this, but I will mention this for others: some say that they don't like processing images
at all because it corrupts them and it becomes less genuine, and this is their justification for using the camera generated jpeg; this is a mistake because, as I mentioned earlier, the image is still processed by the camera which does alter what was captured by the sensor.
Post processing using RAW data turns the control over to the user, so they can have the image exactly as they want it. It may be overwhelming at first, but through experimentation and asking questions, you can become better at it rather quickly. In Lightroom, it is non-destructive, you can't mess up at all because the reset and undo buttons are always there; you have infinite attempts.
What's the general rule of cropping images? I try to compose in frame always but after scanning my 35mm negs, there is the temptation to crop for a more dramatic composition . is there a point where too much is too much?
There is no rule to cropping, aside from any composition rules you may want to keep in mind. Be aware that the more you crop, the more resolution you will lose. With non-destructive editors like Lightroom, the data won't be gone forever if you change your mind but that's not an advantage if you're cropping out a part of the image you didn't want there in the first place.
Once you are able to picture how you want the final image to appear before pressing the shutter button, you will find yourself cropping much less (though sometimes it's unavoidable) or not at all by getting it right in-camera. You will also, by the same virtue of knowing what you want beforehand, be much quicker at post processing, knowing exactly what you want going in.
This takes time and practice, but it is another rewarding aspect of photography.