Yes get that thing back to stock as soon as you can. All that extra stuff is just going to confuse you in the end. There is way to much stuff to adjust and that can go wrong. When you crash and destroy a main blade or two you'll be buying 6 blades instead of just 2.
As for what to use the HK stuff will get you flying for the least amount of dollars. Align stuff will get you into advanced flight and will cost you more but you will have the assurance of high quality parts that are everywhere. Your last option is in the middle of those two, Tarot is better than HK and not as good as Align but will save you money over Align and be a little more than HK. Of course this is just another option.
As for the tail you will want to get that back to torque tube as soon as possible also. The last thing you need is a brushless motor going out mid flight. The motor will cost more than a gear set. The black Align gears have been one of the top upgrades for the older kits. If you don't feel comfortable with torque tube then go with a belt conversion kit. I think Tarot has one, the down side is that you will be replacing everything from the front boom block all the way back. This will also take the tail back to a 2 blade setup which is all that is needed.
If you happen to make the conversion back to the original sport v2 keep all the other for later in case you want to get into scale flying which is what that set up is really for.
just ask your questions so that you can get off on the right foot. We are here to get you going safely and as quickly as you feel comfortable with. Pics and video will help out immensely. Its easier to trouble shoot a video than text.
-------UPDATE---------
Tarot complete flybar head for the Sport V3:
Tarot RC 450 Sport Complete Rotorhead
Tarot does have some of the stuff for the belt conversion, the problem is that you will have to piece it together. They also have most of the parts for the torque tube setup. When you are ready to convert the tail back to a direct drive setup let us know what route you want to go and we will help guide you in the right direction.
I will keep updating as i find stuff.