Oh he's adorable! And Marvin does suit him.
Ask around your local vets if they participate in the RSPCA C4 sceme for neutering strays - if they do, you get it free. I usually state I'm going to act as a feeder, then they get registered to me.
If he's sticking around, why not ask about a discount on microchipping aswll? Worth a bit of cheek and if he does wander off, you've got a better chance of getting him home safely. I'm so jealous, he's just lovely