Should I use most simple or simplest to indicate something cannot be more simple? Can I use both? Is one prefered? If simplest - how is that pronounced? (Is the e silent?)
The only case in which I could see any of them causing confusion would be if the person you were speaking with was only just beginning to learn English as a second language and might only be familiar with some forms of the future tense--in which case your choice is almost certainly the simplest even if it isn't the most nuanced.
This article has an extended list of words with silent and pronounced "l". For a language learner, the simplest rule is remembering some most commonly used words that do have silent "l": -alk: talk, walk, chalk; -ould: could, should, would; -alf: half; -alm: calm, palm; Pronouncing the rest of the words with "l" articulated is not necessarily grammatical, but certainly more accepted/understood ...
I think that's the simplest way to describe the difference between these two words that you can possibly come up with.
They differ in meaning, and in register. The simplest words in your list are ahead, front and forward. Forward usually indicates a motion: "Move forward" Front is a side of something, It doesn't usually indicate a motion: "The front of the house" Ahead means "to the front of". You can say "move ahead of me" to mean "overtake" As with many common words, there is overlap, and secondary meanings ...
It's fundamentally the same as the rule in Spanish, which is usually regarded as having one of the simplest orthographies ever. One of its biggest irregularities is that C and G do one thing before I and E, and another before A, O, and U :)