Manhattan is, without a shade of doubt, the most powerful superhero in his context. In his world, there are not other being with powers like his own. However, other mainstream superheroes are probably mightier than him, since they can achieve feats he can't.
No. There are far stronger heroes that use magic, can manipulate reality (some on multiversal scale) and are less limited in terms of capabilities. But that's because Moore never meant Dr. Manhattan to be the strongest.
Manhattan's powers grew exponentially and he was able to surpass his limits by being able to use reality-bending powers, having free will and being able to intervene. So, the character evolved and with that evolution, his powers grew to a practically unfathomable level.
If you just want to show it on the internet and on social media, a good canvas size for digital art is a minimum of 2000 pixels on the long side, and 1200 pixels on the short side. This will look good on most modern phones and pc monitors.
“Hi there, I'll be missing practice today. I couldn't really think of an excuse, so I figured I would just tell you straight.” “Thanks for understanding.” No excuse is good enough to miss practice.
"All" is not a proper noun. Only proper nouns (personal names) are capitalized. Note, when ending a letter, the proper grammar is to use "Best regards," or "Thank you,".