Much advice here. I'll throw in my 2 cents:
Island, or around the walls: Part of this depends on how / whether you want visitors to experience the layout. Visitors will not be interested in duck-unders to reach the center of an around-the-wall layout. As it is now, people can congregate around the edges.
Big oval or E-shape: The E-shape yields a longer run and makes it easy to include reverse loops (since your train is already reversing direction at the ends of the "E". But in a room this size, it will limit your max curvature. It becomes a question of whether you are more interested in "operations" (the number of things your train can do) or appearances (more realism through gentler curvature and longer straightaways).
Yard design: A yard should have a designated arrival / departure track. The departure track is where the train made up by the switch crew is placed so the road engine can couple up to it. The arrival track is where the train that has just entered the yard is left when the road engine goes off to be serviced, while the rest of the train is handed over to the switch crew to be broken up. This track needs to be long enough to hold the longest train you intend to run. In a small yard such as yours, one track will serve for both arrivals and departures. It also needs to be double-ended, so that, whichever direction the train is traveling, the engine is able to "escape" from the end of the track. In the yard you have drawn, if you made the top of the two purple tracks double-ended, you could use the bottom red track as the A/D. The locomotive would escape from either end of the red track, then back down the purple track to reach the switch to the turntable. The purple track would also serve as a "runaround" so your switch engine could get from one side of the yard to the other.
If you have your A/D track, and the purple "runaround" track next to it, double-ended, the rest of the yard doesn't really need to be. It is nice to be able to get at things from both ends sometimes, but if you are short on length, consider only having those two tracks double-ended, to get more storage space for cars. It will also save you money on switches.
I agree with others - make the yard longer! Yards are never long enough!
I am not sure what the pink connection to the turntable is for. Is it to change engines on the trains in the passenger station? If so, you need to change things so as to get the engine to/from the station with fewer changes in direction. The way you have it now, moving engines back and forth will get old real fast. It's just too fiddly. Try to get that crossover right at the train station throat, so the engine can go right to the turntable.
If the pink connection is not intended to serve the station, then I would just nix it. There is no other reason I can see why an engine would need to enter the terminal from that spot.
Reverse loops: Reversing direction can make things more interesting, but at a cost. The loop eats up space. It is also not realistic. Real railroads run trains in the same direction for hundreds of miles. Because you have a two-track main line, you already have bi-directional running, and do not need a reverse loop in order to achieve it. As long as trains on either main line can reach the yard, the train can terminate, and the engine can run in the opposite direction with a new train (or even the same one) if you like.
Wye: For all the same reasons you don't need reverse loops, you also don't need a wye. It is true loops and wyes give you more options. But do you need more options? Some people like to vary the route of the train... just because. Others want the train to "do something" and so build in the options which are conducive to the operations they want the train to do, and leave aside the other ones. Sometimes variety is the spice of life, and sometimes variety is just bewildering, and actually takes away from the fun. You will have to think about which camp you fall into on this one. Full disclosure: I am firmly in the second camp.
Double crossover: Make no mistake, these are cool as heck. But you really don't need this one. You need two single crossovers--one at each end of the yard. These will also create a passing siding, which you may want. You also want one more single crossover between the passenger station and the pink turntable connection.
Sidings: I see by the arrows that you are set up for right-hand running. But this means that your sidings you have planned in on the right side are all facing-point. That is, the engine enters first; you can't back the train in. A facing-point situation is difficult to switch--impossible unless you have a double-ended siding nearby. Consider making the sidings point in the opposite direction. Or else consider using left-hand running (like the Chicago and North Western).
Sorry I did not reply a second time to your turntable thread. I'm glad I saw this one. I hope this does not sound too pedantic! Really just trying to be helpful, and to explain myself. Enjoy your layout, however you build it!
Thanks so much! This is such a big help and exactly the sort of info I have been looking for!