A few fuzzies at a time sounds like a reasonable recommendation from your vet in my opinion, but I can't really say anything beyond the fact that I personally see no issue with complying with his recommendation as I am not a vet. In general, feeding multiple smaller prey items is not harmful to snakes. The general recommendation is to feed only one larger primarily because not all snakes will accept multiple items and the debate on which takes more effort for the snake is currently leaning towards one larger item being a bit less taxing than multiple larger, but that assumes both are fully developed rodents. In your particular case, it sounds like (in my opinion) feeding a few fuzzies would have potential real benefits without any increased risk vs feeding a larger item. I would start with the lower end of the vet's recommendation and work towards the higher end. (i.e. feed the two smallest fuzzies you have first, then two that can be a bit larger, then three fuzzies, or something similar) Keep an eye on him and make sure he's passing waste properly.