when and what to use

Weed n Feed is rarely a good choice for any lawn. I can see using it once or twice on lawns that are full of weeds. But even then, applying a spray herbicide is more effective. And using Weed n Feed every year or multiple times a year because you have a few weeds is nuts. If you have a healthy lawn with dense turf, you will have few weeds and they can be dealt with easy with a tank sprayer, delivering the herbicide to the few spots and right on target, instead of broadcasting it all over the place.

For spring fertilizer there are all kinds of fertilizers available in at least a couple of categories that are formulated for turf. The chemical based ones are a lot higher in nitrogen (the first # on the bag) for fast green up. Organic ones tend to be lower in nitrogen, but may be better for the lawn. It also depends what is available locally and the cost. Also be sure to factor in how much N P K are actually in the bag. They are listed as percentages. So a 40lb bag that has N of 32 is the same amount of nitrogen, 12lbs, as an 80lb bag that shows N of 16

The other choice you have is whether to put down pre-emergent crabgrass control. If so, then you most likely want to buy a product that has it mixed in with the fertilizer. It should go down about the time the forsythias start to bloom for maximum effectiveness.