Same Side vs. Alternating Legs
Google "reverse lunges" and you'll see a mix of reverse lunges done with alternating legs (left, right, left, right) and others lunging back with the same leg for the whole set.
Those people are just doing what they prefer, but there's actually a reason why you might alternate or choose to go with one leg at a time, and it's pretty obvious if you think about it.
Alternating legs is more unstable. It requires a mini-reset at the start of each rep which requires extra balance and coordination. But it also causes a loss in tension. So while alternating legs is great for stabilization, athleticism, and offsetting some fatigue on each leg between reps, it might not be as good from a physique development standpoint.
Reverse lunges performed one leg at a time are more stable. There's less chance of lining your limbs up in goofy positions, and more of a chance to feel that tension through those targeted muscles.
Neither option is better, but you should be picking the variation that's more closely aligned with your goals.
A deficit is for a deficit! If you're elevating your front foot in order to lunge lower, then your knee should drop below the point where it would be hitting the floor (without the deficit). If it doesn't, then there's no reason for it.
A deficit isn't for everyone. If you can't do a pristine reverse lunge without your back leg cheating the lift, or without your back knee almost kissing the floor, then you have no business doing it off a step.
Adding a deficit works to take you into a deeper range of hip flexion. This loads your glutes in more of a stretched position and arguably activates more of the "lower" glute fibers (gluteus maximus).
Choose the range of motion that helps you avoid pain and allows you to feel your muscles doing the work.
Keep your back leg from helping too much. Reverse lunges are a single-leg exercise. That means they should allow you to focus on developing one leg at a time, with very little input from the other side. But that's hard to do with reverse lunges. You need to pay extra attention to what that back leg is doing.
Two-thirds or more of the weight should be traveling through your front leg. And that really is the absolute minimum. The back foot is there to allow just a little stability as you lunge back. Your front leg should be getting hit the hardest.
Depending too much on that back leg cheats you out of progress and doesn't do your knees or hips any good either.