1) I don't really have too much of an issue with any of your items. The scroll sealing system was, in my mind, designed to outline the limitations of scrolls and provide more of a guideline for other sealing methods. Your body sealing idea should also not be too much of an issue as long as it's kept reasonable in terms of quantity and power. Can't have you sprouting an infinite amount of weapons from every inch of your body or anything like that.

2) You aren't limited to just scrolls, they are just the most common. You'd have to write up Jutsu and Equipment descriptions for your body sealing techniques for me to judge individually whether they are appropriate but initially it seems fine to me.

3) You answered your own question. The reason scrolls are capped at 50 ninja tools is simply because any more would be OP. I don't think you comprehend just how big of a number 50 is when it comes to shuriken sized projectiles. Quantity over accuracy isn't true either, that's why we have accuracy based Special Characteristics. The point of those SC's is that no, any random person CAN'T just dodge your projectiles because you are just that good which makes sense if a person has dedicated their life to projectile weaponry use. Your idea of different scroll types is interesting and I'll definitely think about it though.

4) Sasuke is the very definition of Canon being OP in a roleplaying context. The proposed jump from 10 to 100 is a big deal and probably wouldn't be allowed since it's far too great a number. You also wouldn't be allowed to seal such a seal into a scroll as that's far too similar to sealing a scroll within a scroll which we don't allow.

Hope that answered everything.

How is the cost giant? 1 CP to unseal the scroll? It's 1 for the entire or part thereof contents of the scroll, not 1 per item...

As for Tenten, no.....she was one of the few members of the Konoha 12 who WEREN'T overpowered. That doesn't make her weak, just normal. It's easy to say that she's weak when compared to Naruto, Sasuke and Lee who were all capable of things they shouldn't have been and Neji and Hinata who she naturally has a disadvantage against because of Hakkeshuo Kaiten and the defense it offers. Compared to people like Ino, Chouji, Shikamaru, Kiba, Shino and Sakura, all shinobi of equal rank to her, Tenten is just as capable in combat.

As for your S Rank example, if the scroll user has sealed E Rank weaponry in their scrolls then they've handicapped themselves in the same way that a Ninjutsu specialized Jounin would be if they spent their battles spamming C Ranked techniques. Considering they're capable of wielding at least 5 S Rank weapons and the power that S Rank weapons can have, I'd argue that simple dodging would be useless.

Once again, you're downplaying just how significant pinpoint accuracy is. Against someone equal to them in rank, a weapons specialist with pinpoint accuracy would be very difficult to counter. Why? Because short of having speed increasing SC's or utilizing defensive techniques, the weapons specialist can launch their projectiles with such quickness, velocity and predictive aiming that simply dodging is very difficult, if not impossible. To suggest otherwise would be bordering on GM'ing.

You do realize that each small scroll is fifteen centimeters in height right? 50 Of those would definitely be of no small weight nor would they take up less space than 1 giant scroll that is one meter in height.

Your opponent is obviously thinking too highly of himself then. Having precision accuracy and a quick draw obviously doesn't guarantee 'one shot one kill' situations but it certainly means every projectile thrown has the capacity to kill, regardless of size. Projectile weapons in the hands of someone highly trained in their use became far more dangerous than they would be when used by a regular shinobi in the same way that a sword is much more dangerous in the hands of a swordsman than a regular shinobi.

Tenten wasn't OP because her abilities were not beyond those that should be available to her rank. If we use her fight against Temari in the Chuunin exams as an example though, you'll notice two things; Firstly, her scrolls are well beyond even a gigantic scroll in length yet still have the same height as a small scroll so obviously they aren't just standard scrolls. Secondly, your figure of 400 weapons is far too exaggerated. Looking at the number of projectiles that Temari actually deflects, those two scrolls held no more than 25 weapons each.

The methods you mentioned also aren't loopholes, I've noticed the possibility of such things and purposefully left them unchanged because, in my mind, someone experienced in sealing should have little problems sealing multiple items in a single more powerful seal. Also, the creation of custom Jutsu for any of the specializations is really only limited by the abilities of your character, the guidelines of the site and the creator's imagination. At some point your argument became less about any massive issue with weapon sealing and more about your personal preference when it comes to what can be done.

Also, regarding the storage technique, my interpretation is that the cost applies to each use of the technique, not each item sealed or unsealed. There may be staff that disagree with me though so I wouldn't take my word as final.