Yes, for example: In fact, a few species of birds are flightless.
Yes, I can start a sentence with "Is."
No it isn't okay to start a sentence with but. Just add what is after but and turn it into a compound sentence
No. There is no word in English that cannot start a sentence.
No it won't, unless it is at the start of a sentence.
Well that is a tricky question but i would say at the start of a sentence people would often use "I" at a start of sentence. There is loads of words to start a sentence so i can't tell you all of them obviously. example: "I" went to the shops to buy sweets.
start of with a in coming shock and fact
a sentence that tells a fact is a declarative sentence
Despite the fact that money was counted three times, it still fell short of the correct total.
It's a fact! Your accusation is not a fact!
No, you cannot start a sentence with "no" unless you need to do so. No reason exists not to start a sentence with that word, as you can see. No one will care if you do start a sentence with it.
I like guys in fact I only like guys.
a declarative sentence is a fact
Some would question that fact.
Opinion
"I love cats, and as-a-matter-of-fact they love me too!" is a sentence with those words.
You can start a sentence with "Also"
A fact sentence is a sentence that states a fact (something known to be true). Some examples are: The earth is round. The force of gravity is the reason things do not float off into space. The sun is hot.