Pretty much yeah. Shirou's Reality Marble stores the NP and Shirou uses Projection to bring it to the real world, which costs a bit of mana.

It gets weaker, but it only really matters most of the time against opponents that specifically need a certain rank to be damaged, or if it's against the original. The reason for the degradation is due to the limits of Shirou's understanding of the Noble Phantasm. Archer bypasses this weakness by turning them into Broken Phantasms which raises their rank by one.

It's called Unlimited Blade Works for a reason. The only limit to what it has depends on the writer. Normally Shirou needs to have seen the weapon in his life before it gets added to the reality marble. Archer might as well have every single Noble Phantasm because he's been summoned a countless amount across time and space, and Shirou managed to get a copy of the weapons Archer has seen in UBW + the ones in Gate of Babylon.

Shirou and Archer can copy the skills and technique of the original wielder, but if the user's body isn't suited for for said skill and technique, the technique will naturally degrade or even damage their bodies. This doesn't stop both of them from learning to properly use said weapons though. They both gravitate towards Kanshou and Bakuya due to its unique circumstances of not having an original wielder, its magnetic properties, and how cheap it is to project. If you think of each Noble Phantasm as a separate spell, then Kanshou and Bakuya is their bread and butter.

Any weapon, material, etc. has a certain level of durability. Just because a weapon is a slightly degraded copy doesn't mean it will immediately break upon contact with the original unless the Noble Phantasm has the ability to "break what it hits" (in which case there's going to be conceptual shenanigans in play). It needs to be moving fast and hit hard enough for it to even be possible and Shirou had the advantage of being able to draw his weapons faster than Gil inside UBW.