Interesting question, as the two are actually related. As a general rule, certain pawn formations such as doubled or isolated pawns become much weaker in the endgame than other phases of the game, which is the main reason to avoid them in the first place. Remember that the pawn structure you create in the middle game is something you may have to live with in the endgame, so plan accordingly. There are exceptions, and certain pawn formations can be losing even though they dont appear to bear the "germs" of defeat. One such example is White pawns on a5, b5, c5 Black pawns on a7, b7, c7. Now, even though the black pawns are not "weak" white has a breakthough here: 1 b6! and if: 1...axb6, 2 c6! forces a queen. Similarly, if 1...cxb6, 2 a6! forces the same result. This of course is a tactical example, but remember such things lie beneath the surface in many positions that are otherwise "equal".

The second part of your question also depends on pawn structure. In a position with wide open lines (or diagonals) a bishop is usually preferred as it can cover more area and travel from one end of the board to the other in a single move. However, in a more closed position (such as white pawns on c3, d4, e5 and Black pawns on c4,d5, e6) a knight can be preferable because of its ability to hop over pieces and to control squares of either color.

I suggest you find a friend or and play out different endgames, some with blocked pawns, some with open positions, some with bishops, some with knights, and get a feel for some of the ideas in these endings. Study the games of masters and see the ideas the use to win (and draw) these endgames. Do this in slow games or untimed games so you dont have the added pressure of time to distract you from working through the possibilites.

The best answer is: that depends. What kind of player are you? If you are a go-getting attacking player, certain openings will be more attractive to you. If you are the quiet, positional type, then there are openings that will make you feel comfortable in that regard. A mistake many people make is to think that a certain opening is for certain types of players. For example, there are lines in the Sicilian that are certainly doubled edged where everything hangs by a thread. On the other hand, there are also lines in the Sicilian that feature quiet maneuvering. So it is not so simple. My advice is determine the type of MIDDLEGAME you seem to feel comfortable with (do you like open lines or kingside attacks or stable centers or closed positions?) Then, once you have a feel for that, choose an opening variation that leads to those kinds of positions and play that.

Another thought on openings; I find that many beginners (and some NOT so beginners) have the feling that they must know a dozen variations to every opening they might meet. This is time-consuming at best and dilutes your efforts at worst. I am reminded of a story that illustrates the difference between lower and higher rated players. An amateur magician came backstage after an impressive performance by a professional magician. "I do 100 card tricks!" he bragged. The professional looked at him and said "I do only ten----but i do them VERY well!" Be like the professional. Choose one or two openings and know them inside and out.