I'm not sure how logical it's to give Walter money instead of the photos. In principle Walter doesn't need the money, but in the first mission it makes sense to pay him, while in the second the alternative options also seem logical. But in the mission where Walter wants the photos for himself, without him actually asking for anything specific in return, it doesn't seem reasonable for him to accept money.
Possibly the other option
randomguy6516265165 has proposed is more reasonable: give him photos downloaded from the internet (perhaps from a payment page, to make the MC spend some money and justify that Walter doesn't find or know them)
I think the MC's personality is very well achieved. I like how he is evolving throughout the game. If we add to this that I generally like LIs quite a bit, it seems like a great game to me.