Interview Question - Freshman at a Non-target

I'm a Freshman at a Non-Target, and I networked fairly well with an alum who's in charge of a sell side ER department at a boutique, and he conducted a phone interview with me this morning for an ER internship.

Honestly it was probably one of the best interviews (phone/in person) that I've had yet. He knows that I'm a freshman and doesn't have a problem with it since I have previous work experience, and I was able to strongly sell my story to him. The only bump that came up was that the position requires modeling excel knowledge, and I was upfront with that I don't have that knowledge, and my excel skills are only basic/low intermediate range.

I told him that my UG offers free excel workshops (1-4 hours each for 1 day), and I would be open to taking them. He had me send him a list of the courses offered and got back to me with the ones that I should take. In total its 4 courses. He told me that if I had those courses under my belt he would teach me how to do the modeling the internship requires.

Now, that sounds awesome and like a great deal, but I don't have a formal offer yet. I know that taking those courses would benefit me anyway, but should I sign up for them and take them without having a formal offer yet? Right now our correspondance is for me to reply to the e-mail where he pointed out the courses I should take, so I'm not sure how I should reply. We also already discussed compensation and hours/week I would be open to taking on.

Thanks