I don’t have a RecTeq, but might have had a few pellet grills over the years. I like front shelves, they make getting food off and on, wrapping things mid cook, etc. easier. Upper shelves depend solely on your capacity needs, with the fan it’s going to be about the same temp there as main grate. Are their sear grates GrillGrates? If so, I sometimes use them but I don’t love them. I think they are a PITB to clean. However, if it will be your only grill, definitely worth it to help with searing and also be sure to try them flat side up. Lately, I’m playing more with cast iron on the grill because it holds more heat and I’m not a believer that grill marks taste better than an all over sear.
Not on your list: If it’s regularly windy or rainy where your grill will be, the vent extension thingies they sell might be beneficial.