Ah, I remember when I first picked up a stick. I was terrible!
As for the transitioning from pad to stick, I was in the same boat you were. Always used pads, never really got a chance to play stick. However, keep in mind that you will have to relearn all the basic inputs. Fireballs, DPs, ultras, etc. However, depending on how familiar you are with these inputs, it can either be pretty easy or pretty hard. Let’s assume you’re pretty familiar with said inputs.
No matter how familiar you feel you are, stick is quite a big change. At least, it was for me. I was already an okay Street Fighter player by the time I bought my stick, so I already knew the inputs and such. However, performing them was really awkward at first. It took quite some time for me to get used to, but that might differ for you. My advice would be to hop right into the training room and practice these inputs. I decided that I would practice the inputs until I was able to get my moves at least 10 times in a row without any trouble - then I would move on to the next one and, from time to time, re-visit the previous moves just to make double sure that I got them. If you choose to do it this way, make sure you practice on BOTH sides of the screen. Which I’m sure you know, but I thought I should mention it anyway.
Also, find a way of holding a stick that is comfortable for you. There are a few different ways to hold the stick, so experiment around with that. I, myself, feel most comfortable holding the stick like Daigo. It just feels right to me.
Once you feel comfortable, I still wouldn’t recommend jumping straight into a competitive match. Instead, I suggest playing a few matches against the AI (eh, you don’t have to, but it helped me.) just to get used to using it in a match. You don’t have to play too many, just a few to get a feel of how an actual fight with it could be.
But, keep in mind playing on stick might not be for everybody. I honestly like playing on pad more. In the end, it all boils down to personal preference. It’s not like a stick is a magical device that makes you a godlike player. It’s just another tool to use. Now, I can still play stick, but unless I’m in the local retro arcade at the SF machine, I’m pretty much always going to be playing on a pad. It’s just much more comfortable to me.
Hopefully I helped a bit and didn’t just ramble on too much…