To your point about titles, if you can envision giving him that large an equity chunk, especially in lieu of salary, I would have no problem calling him a founder. And in your shoes, for the right guy, 35% might be fine for someone to come in full-time. Seems a little high given where you are, but I'm just saying it could be fine.
However, I would consider what he's proposing as part-time, no matter how many hours it is, if he has another job. That's not ideal, but again, for the right guy, maybe it's ok for him to not commit fully to your company. But I would say if he's worth 35% full-time, he would get 17.5% part time. Maybe not exactly half, but hopefully you get my point. You could structure it so that his stake increases some amount when he joins full-time. The longer he waits (and the less risk he takes), the less the increase, in my opinion. And vest everything. For yourself too, for that matter.
I would say to iron out expectations with him. For instance, it sounds like he's expecting a market salary right after funding. I would not expect that, especially if he comes in as a founder. Same sort of thing as wanting to get preferred stock.
He sounds risk-averse, which is fine, and understandable. But if so, you might find the conversation a lot easier once you have actually closed some pre-sales, if that is imminent. Doing that will show him that there's a lot higher chance he'll get something back for his investment. Good luck!