I'm no expert but here's what I've learned:

I don't think you'll be happy with 4" lights - they're pretty small.

Typically you want to place them over the edges of your counters which is probably 24" away from the wall. This way you're not working in your own shadow and the cabinets won't block light onto the counter top. Every 4 feet or so is pretty common for spacing - do whatever looks right. You'll want task lighting at the sink and in prep areas, and any other dark corners that might be in your space.

You can take your kitchen plans to any lighting showroom and they'll typically help with lighting design.

I found this thread helpful when doing my own project.

We used halo LEDs - make sure to ask for warm light (2700k or better) otherwise your kitchen will end up feeling washed out and clinical.

Here is a link that might be useful: LED recessed cans guide for kitchen ...