For glitter and additives, I always apply them to the 2nd coat of colour after its been under the lamp, the tackiness of the inhibition layer is enough for products to stick to it without disturbing the actual colour underneath, I know a therapist at my work chooses to apply glitter to the second colour coat before it goes under the lamp. As for foils I haven't tried them yet, but I'm hoping to soon!
I love the lacente glitters, super smooth and sparkly. I bought a pack of cheap glitters off of Amazon to try and I must say that some are really good quality but a few are too rough so even with 2 coats of top coat, you can still feel the grittiness of it, which isn't the best.
HTC x