Personally, PEA gives me a mild & very euphoric kind of energy.
1,3 is very clean as well, but provides a bit more energy, but is pretty euphoric/mood enhancing at the same time.
Phenibut gives me a good clean relaxation type of feeling, which also makes me a bit tired, but it is great for good quality sleep. Personally, Phenibut is great for relieving anxiety and a good "perk me up" on those more stressful days. You just definitely shouldn't take Phenibut everyday, for it will make you deficient on naturally produced GABA. 4 days tops per week, with at least a 3-4 day wash out. Trust me when I say that is NOT a good feeling if you take it for too many days straight!
And, to help answer your question, yes, I feel about 60-200mg (tops) of Caffeine would stack great with PEA, as many products with PEA also have Caffeine as well. To help the life span of PEA in your blood stream, it has been suggested to also take Hordenine as well.