[is the silver spartan hunting john?]

He is hunting John. In the E3 The Master Chief Collection trailer Arbiter is telling him how to find Chief while he is looking at Chief's progress.

[Will Halo 5 actually feel like a Halo?]

It may just be me, but I didn't enjoy Halo 4 as much as the originals. It really didn't feel like a Halo to me. The only thing I can do is hope Halo 5 is better. (If Halo 5 turns out like Halo 4 my friends and I are going to burn our copies of Halo 4 and 5 and convince ourselves Chief dies at the end of Halo 3)

[Arbiter will return for sure]

Arbiter may return, or they will just show the spartan find Chief assuming that the Arbiter and his conversation had already happened.he may be in a cutscene or two, but I'm almost 100% sure he will not be a playable character.

[The Arbiter for Halo 5?]

There is a possibility for the Arbiter to be in Halo 5. However, he most likely will not be a major character. In the Master Chief Collection trailer you see whoever this new guy is talking to the Arbiter. This could be a hint to Arbiter being in Halo 5 but he will definitely not be a playable character. I'm guessing when you play cooperative campaign the second player will play as the new guy while the first playing as the Chief. As much as I wish he was the Arbiter will most likely not make an apearance in Halo 5. If he does he will probably just apear in a cutscene.