I hope you have not yet made your decision yet, however, I believe partnering up with this individual in 60/40 split will be a mistake. Here are my reason why:
1) This business is yours. You started it and you have grown it to what it is. He is an outside investor, who, not only wants to change the vision of the company, but he also wants controlling interest. The likely outcome is that you two will butt heads on decisions and directions of the company, but you will be powerless because he owns the majority share. He can also have you removed.
2) Being a first time entrepreneur can be tough. Ofter you're doing things you have no idea will work, and its easy to feel like you could be making the next huge mistake that will destroy your business. My guess is that you feel this person can help remove that uncertainty because he is experienced and has connections. However, the odds are that he also does not know what he is doing when it comes to the specifics of your business. He is just going to come in with preconceived notions based on his past experiences and successes. Odds are he can be just as wrong as you can be. You have to trust your gut. Only you know what is best for your business.
3) If you give up the majority of your company in the very first funding round you put yourself at risk of not being able to raise additional capital in the future. If you do raise capital later, you will have to give up even more of your minority share. Venture Deals by Brad Feld and Jason Mendelson is a great book to learn about raising any kind of venture capital and the typical pitfalls.
I can list a few other reasons why this is a bad idea, and I'm happy to jump on a call with you ,should you want to discuss this further.
My advice is you should continue to build your business (slow and steady) until you are in a much better position to raise capital on your own terms and giving up only minority share in the company. One way to start this process is to start charging more money to your clients. I've tried this many times, and it can be made to work. Let profits drive your growth. Raise money when you least need it.
If you must partner with this individual, then I would say a 70 / 30 split in your favor or better. Or an even smaller share and give him the role of an advisor. Just don't lose majority control. this is your business. He should be working for the business, not YOU working for HIM. If you want to work for someone, then then there are less riskier options than starting your own business.
Hope this helps.