If I remember correctly your bunny is young- and that can account for the higher activity.  I have never used a harness/leash on my bunnies- as I am too afraid to take them anywhere on it.   If your bunny is very active he might be more likely to panic on the leash once he gets to the end of it. 

Trying to jump the NIC cubes could result in an injury if he gets a foot or toe caught- I would try to discourage that by lining the inside with cardboard or coroplast maybe?  I have not had that problem with my buns- but if your bun jumps, tries to climb the grids, gets a foot caught and falls off- it could easily result in a broken bone.

Hay cubes are OK as treats- but regular hay is better and there are longer strands of fiber in the regular hay than the cubes. 

Oh, so you are saying that really the only exercise he gets is inside of his pen. If that is the case then yeah, even as large as his pen is (as seen in the other thread – it’s great) he would also need some time to run and get out that energy. Especially when he’s young as even adults need a minimum of three hours.  

Do you have another place he can safely run that you can block off areas with an xpen?

Regarding the leashes, you will find differing opinions and experiences about this. If you do use a leash, only use the harness kind. Also be sure to test it out first in the house. You don’t want to take the chance of him getting free outside. Also, if you do take him outside, you need to be careful that he doesn’t bolt or panic and hurt himself – this can cause major injury. Katnips concerns about him being young and active are definite reasons to be cautious.

The first way to get him comfortable with a harness is to just put on the harness part first and let him get used to it without it being on the leash, then use the leash but let him get used to it indoors. That way you can assess his reaction and decide what is best for him. I don’t know what the “outdoor atmosphere” is like, but obviously you will have to take that into consideration – noise, other animals, other people, etc. My bunnies enjoyed tharness, but t I also only took them into a large isolated  fenced in area where no pesticiides were used, and no animals or other people could easily approach without me knowing way ahead of time.

Also, if you take your bunny outside, you will have to watch for fleas and make sure they don’t nibble on things they shouldn’t.

If you do decide that outdoors is just too risky, then he will need exercise indoors – somehow.  Is there anyway to house proof  your home to make it safer?  Let us know what your challenges are and maybe we can help find solutions.  I know with cords, there are a variety of cord covers you can use, and what are the small appliances he could actually knock over? Is there anyway, that if they are small enough, they could be put up while he plays?

I would recommend finding a room that you think has the least amount of bunny chewable items and block it off with a baby gate – then you can at least sit in that room with him and watch him have some run around time. Also, if you can get an ex-pen, you can open it up all the way and let him have some run time inside that. For some reason, when I put a big cardboard box in the middle of the ex-pen they especially like that because they can run circles around it!