Need Advice: Food, regurgitation, and transitioning

I am currently feeding my cat "Wellness Complete Health Indoor Adult Cat Food - Salmon & Whitefish Meal Recipe" and, throughout the week, a couple cans of Wellness wet food.

My cat has been regurgitating more often than other cats. For instance, last week he regurgitated three times during the week. (There was construction going on which caused stress, but I still think that is a too frequent.) There have been weeks without construction where he has regurgitated more than once during the week, so I am concerned. (Other than the regurgitation, his behavior is normal: Regular sleep and play activity.)

I am using the term "regurgitation," because it is cylindrical in nature and there are whole pieces of food amongst the contents.

Does anybody have any thoughts regarding this?

Should I switch him over to "Wellness Complete Health Indoor Adult Cat Food - Deboned Chicken and Chicken Meal Recipe" - (Could the fish be an issue?) Also, in the store, a clerk suggested that the food may be "too rich" for him. Is that actually a thing? 

Finally, I have read a lot of information regarding wet food and its preference; I do plan on incorporating more wet food into his diet. (I started this week! He had a little diarrhea today, though.) I will still be giving him some dry food, though, which leads me to my next question: Does anybody have any knowledge regarding Simply Nourish Indoor Cat food? Financially, it will be difficult to provide Wellness dry and Wellness wet. Simply Nourish cost less which would allow me to purchase more wet food. (Of course, I would also be interested in other dry food options with a similar, lower price range.)

I apologize that there are multiple questions. Any answers (one or all) will be greatly appreciated. Thank you!

How far apart are the meals? Maybe acid ingestion.

Generally, his daily amount of food is out all day. He likes someone to be in the room, though, so he’ll eat more when I come in. And the regurgitation always happens shortly after eating.

Often cats will throw up shortly after eating if they eat too fast.  One of my cats used to upchuck his food once in awhile, so I put him on Sensitive Stomach food.  That seemed to stop his issues.  Then I switched all of them over to canned food, and that REALLY stopped his issues. 

As far as Simply Nourish, I feed my cats Simply Nourish canned as part of their rotation.  I think their kibble is an ok food, as kibble goes.  It's fairly high in carbs, which I'm not fond of, but most kibble IS.  (even Wellness)  And yes, there is such thing as a food being too rich for a cat, if they aren't used to it   That's why when you switch food, particular dry food, you need to do it a little bit at a time

If he is already showing signs of diarrhea, you might try adding a probiotic to his wet food.  It sounds as if he is a nervous cat.  Perhaps the probiotics will help keep his "gut" on an even keel.  I give them to my gang every day just to prevent issues.  1/2 capsule in the morning and 1/2 at night, mixed into their wet food.  This is what I give them (the same thing WE take)