How old is your barn now?     If it’s already 20+ years old I’d question the value of the SS gating vs how long you think the building will be in use.      There eventually comes a time that even the concrete starts to crumble. Not just the slats and beams, the actual walls that the building sits on.     40-50 years is a long time being exposed to hogs and manure.    We have a 53 year old building, the concrete is really showing its age and will probably be what eventually puts the building out of service. It should have happened prior to Covid blowing up the cost of a new building but who saw that coming.  

I would suggest SS feet or plates on the gate posts though.   Taking gates or posts out to weld new plates/feet on them after 10 years gets old.  

As for the feeders, I would recommend a good shelf feeder (Crystal Springs, SDI, AJ Omara, etc) over those.  .    That is just a tube feeder with more feed capacity.     I like tube feeders but I wouldn’t spend money on new ones.  If going with tube feeders there’s plenty of good used ones out there that can be bought for scrap price. The Original “Aqua Tubes” are very well built tube feeders.  Just make sure that if you do use any sort of tube feeder you need enough tubes so you have no more than 20 hogs per tube.  25 hogs per tube is not enough feeder space and will limit growth.  

I hate plastic mats under feeders.  A concrete pad is better until it gets worn out and needs to be replaced.    Slat coatings under the feeder are better but not perfect either, the water/feed waste still wears on the sides of the slats as it runs down the slat into the pit.  
  For slat longevity the feed and water should be 10’ away from each other.   But that isn’t ideal for hog growth.     Not sure what the real answer is there.      I’ve often thought a concrete slat dipped in plastic might be the answer but I’ve never seen that done.