Congratulations on your decision to learn to play the guitar. It is a difficult instrument to learn in the beginning but it gets easier as you develop some basic skills and start learning the basic chords and strum patterns.
One of the most challenging things to learn for many beginners after mastering the basic chords and changing between them, is strumming patterns (rhythm). And the song you are trying to learn actually has a very challenging strumming pattern for a beginner. You might want to try a song with a more basic pattern, but I will explain what is being described in this lesson and give you some tips on the up strum.
1) He said @4.45 onward, "each one rhythm pattern takes up 2 of the chords, what do he mean by that? If it's 2, why is there "UDD"(Up-strum, Down-strum, Down-strum)?
What he means is that there is a chord change in the middle of each rhythm pattern. Each rhythm pattern is DD UD UDD DU. That equals one rhythm pattern. While you are playing that rhythm pattern, you change chords (very quickly I might add).
The chord transition begins right after the first upstrum in the pattern. The third down strum in the pattern is on the second chord. So to answer your second question - he plays Am for Down Down then on the next UP strum he is preparing to change to the F chord in his mind. He hits the Am quickly on a quick Up strum at the first upstrum in the pattern - followed immediately by the F chord on the next Down strum. The rest of the pattern is on the F chord and then the pattern starts again on the C major chord and changes to G after the first upstrum in the pattern. So by the time you have made it through two rhythm patterns, you have played all four chords in the progression and you start over again.
As far as your up strums sounding "loud and noisy" - keep in mind that it takes a great deal of practice (sometimes at a very slow tempo) to get your strumming to become fluid and smooth. You might find strumming easier in the beginning with a very light pick. Also, keep your wrist loose and flexible and strum more with your wrist than your forearm. Don't dig in too deep with your pick.
On the up strums, only worry about brushing the three or four thinnest strings (closest to the ground). The up strum is as much about maintaining the rhythm as it is establishing the harmony by hitting all the notes in each chord. The down strum is where you can emphasize the bass notes in the chord. Be sure to avoid the low E string on the down strum when playing the version of the C major and F major you pictured.
The way you pictured the F major chord in your question is an acceptable way for a beginner to play that chord. Just be sure you are muting the high e string with your first finger. Later you should try to learn to play the F major chord by barring the b and high e string at the first fret with your first finger to add that f note to the chord on the 1st string (play the note instead of muting the string).
For a more detailed discussion on strumming patterns and strumming techniques - read this on Stack Exchange - Strumming Patterns and Techniques for beginning guitarist
Good luck on your journey and keep it fun.
