A couple of thoughts for you.
Whilst I wish you luck in your self inflicted challenge don't be under any illusions that 100km is a very very long way. The vast majority of what would be termed regular walkers could not and would not contemplate attempting such a long distance in one go in one day and very few would actually be able to complete it successfully. The truth is that ultra distance walkers/runners are specialists.
My advice would be for you to take a reality check, take any 'pressure' you may be feeling off of yourself and make sure any sponsors you manage to obtain are sponsoring you per km and not reliant on you successfully completing it.
The pain is more on the top of the Toe / Joint and is stinging on the top of the foot and a pain in the pad.
Is the pain on top of the toe/joint being caused by the top of your toe contacting or rubbing on inside of the shoe above and on top of your toe?
The stinging on the top of your foot may be being caused by you overtightening the lacing of the shoe. Your feet swell after a mile or two and your lacing probably needs to be adjusted/slackened to compensate for this several times or more during any walk.
There are basically two types of insoles available on the market and your decision as to which to choose should be based on whether you are looking for arch support and correct foot positioning (harder and more supportive like Superfeet, Sidas and Sole) or whether you are looking for softer spongier cushioning for your feet (like Sorbothane Double Strikes). The Superfeet insoles need a break in period (around 1-2 weeks or possibly longer) increasing daily wear time gradually over that period whilst your arches, tendons and muscles adjust to being held in a different and corrective position. Check videos on YouTube re breaking them in.
I think you may have possibly made a mistake in choosing the Superfeet insoles as in your situation I would be looking for as much cushioning as possible such as the Sorbothane Double Strike insoles. You need to be aware that the Sorbothane Double Strike insoles are thicker (around 7mm) than most other insoles on the market and take up significantly more room inside your shoe/boot leaving less room for your feet.
You may even find that switching back to using the insoles supplied with your Merrell Moab reduces the pain you feel.
The main advice I would offer is do not wreck your feet trying to resolve this as healing time can be both very painful and lengthy.
If you cannot resolve the issues yourself be prepared to arrange to visit (and pay if necessary) a professional bootfitter for some advice and depending on where you are based you may need to travel a fair distance to find one. (NB I do not mean your local branch of Millets or Blacks etc but a proper boot fitter)