Partial Answer
Prefix: The work behind the prefix is quite a challenging puzzle. The fact that we have to add, remove, and shift letters is quite ingenious. Please do this again at some point!
I think the prefix contains IN; I'm guessing this based on using my mind and keeping in mind. How this correlates to the riddle for finding it, I'm not sure yet.
Sea: Add sea salt for taste. The salt is a waste.
Mind: Use your mind.
It: Wrap it up, choke it down.
Now these have to work in conjunction; I believe somehow we will be combining sea and mind by wrapping it and choking down (removing letters). This is quite a riddle in itself and ingenious on behalf of Cubemaster.
Infix: This has been narrowed down by ... and confirmed as narrowed by Cubemaster; however, a true infix has not yet been found.
X or Ex; I believe it is x as there are more possible combinations, and x literally marks the spot whereas ex is simply another interpretation.
Suffix: The suffix has been troublesome to the entire community, with many answers coming to the light, but alas, all were wrong. I believe it may be:
Synonymous to future in some way; words such as later or fate could be possible. This is a guess based on elusive every day and front of the line since the future is constantly eluding us and is always ahead of us.
Full Word Guesses
First Guess: This one is quite odd, and is most likely wrong. I would be very surprised otherwise.
Mesaxon - This meets the criteria of everything, though most likely not the answer; for example: The prefix is mesa which is the combination of sea and mind when wrapped and choked. The infix is x, and the suffix is on in which a definition denotes indicating continuation of a movement or action which is synonymous to moving forward to the future.
I would really like to see anyone solve this, but it is quite a difficult riddle! Congrats to Cubemaster for forcing us to think to lateral extremes. I didn't know that my body is better at yoga than my mind! I should probably start doing more brain training.