Thanks @KelleyBee . I will go ahead and and get the larger feeders for the grow out and keep the 5" for the does and buck. I am going to go with the bottles for now. Any brand I should stay away from? Have you tried the flip tops?I just recently upgraded my J feeders for growouts to the wider ones. So, I’ve gone from a 4 inch wide feeder to a 12 inch wide feeder and I am so glad I did. If you can afford to get them from the beginning, go for it, I say.
Note: I did not cut open the cages to fit the feeders. Instead, I wire the feeders in. During my initial setup for my main breeder cages, I did cut holes to fit the 4 inch feeders. I will never do that again. Sure, by cutting the holes, the filling side of the J remains on the outside of the cage for ease of filling, but once that hole is cut, adjusting the location of the feeder is no longer an option unless you cover the original hole, etc. so, I will never cut holes again. Besides, opening the cages every time one feeds has more good attached to it than negative: opening the cage slows you down which means more time to assess the resident, to speak, to interact, to make sure all is well. The only positive to not having to open the cage each time we feed is time saving for the feeder. The time saved does not offset all of the benefits gained by the rabbit when you open the cage to feed each day.
I recommend water bottles, but to answer your question about transitioning rabbits from bowls to nipples, the best advice I received when I was faced with this transition is: rabbits can smell water, even in the bottles or in the lines of a watering system. When transitioning, the biggest mistake people make is leaving an easier drinking option in the cage, i.e., an open bowl or the steel ball nipple. The rabbit will always choose the easier course. If you provide the water in the nipple system, provide no other source of water and the rabbit will learn to use it due to not having another choice.
If you’re concerned about algea growth, you can do what I do in warm months: keep 2 bottles per cage, each day remove the first bottle and replace with a freshly filled second bottle, empty first bottle, keep first bottle lid open to air out and set empty first bottle indoors to completely dry out over the next 24 hours. The next day, replace second bottle with first bottle and air out second bottle as described. Do this rotation daily and you drastically reduce algae growth. It also gives you a daily opportunity to look into each bottle to inspect for issues. By following this system, last summer there were only abut 2 bottles that needed extra cleaning efforts.