Also satisfied with Interdeck, esp the 'grip', but it does tend to 'hold onto' dirt. Easy to apply - yes it changes colour with time but in our case now closely matches the rest of our deck (was much whiter to start with but has 'yellowed nicely'
) Pretty sure that Interdeck is just 'Brightsides' with grit so you should be able to blend some colours for a few more options...
Think you can mask around equipment that you can't/don't remove, but better to get under it if you can. On a past project we removed everything but the toerails and winches, taped off around those.
If you have a molded nonskid pattern it can be difficult to properly prepare.. if you don't want to preserve it I guess you could sand/grind it smooth and start over. Otherwise the best prep you can do might be a thorough TSP scrub followed by a solvent wash. If you do use Interdeck it will likely 'hide' the original pattern.
Many here rave about the results using Kiwi Grip, and I've seen some nice results too - it's also tintable to your colour so before committing to Interdeck maybe check that out first.
Non 'nonskid' areas should be sanded properly, cleaned and then probably 'rolled and tipped' unless you're able to spray. You can get a reasonable DIY result with the HVLP blower/spraygun setup that bathtub refinishers use.