Anything too loose will make a person look heavy. Heavier than they are, at times. Too tight fitting clothes really hide nothing. So, I'd say you have to find the happy medium, so to speak.
I wouldn't tug a shirt into the pants too often, it tends to make a person look small and round.
Personally, I'd say everything that's at least two numbers too big... it considered too big in my book.
Yeah, tucking in the shirt in the pants is generally not too good unless you have a jacket that you put over it. Otherwise it shortens your torso to the eye, and that's a stuttering image to the brain lol
As for the picture, I'd say they're a bit too long, but not so much that it's too much, just not my preferred length. I like my short sleeves to be about just past halfway down my upper arm. It gives a good visual of how long and proportionate I am.
As for tightness, well, it all depends.
If it's ripping quickly from wear, too tight in my book. Also, if it takes you a two man team, two tubs of butter and an hour to get into the outfit, also too tight. You also don't want to look like you're part of the Shrine Circus by wearing a billowing cloud. For tightness I would advise what is comfortable, casual button ups are good, even standard tees, enough to accent what you have.
For length, ehh, it doesn't go far past my hips/top of my jeans, otherwise you're moving into small dress area.
Also, horizontal stripes, avoid them unless you're a twig...>.>