Greetings,
1. The size of the drill hits depends on the size of the screws you want to use and the size of the mounting holes to which you will be mounting the PCB.
2. Drill hits are placed by using the "hole" tool in eagle...
Questions like this, along with many other general questions, can be answered by reading tutorials and watching instructional videos. If you are going to be doing alot of board design, I would suggest looking at some of these...
3. You can create polygons in eagle. If you have an empty spot on your PCB, you can create a ground section; you can then connect to this section by routing other ground traces into this polygon or by using vias. Depending on the number of layers in your design, you might want to consider using a ground plane. This will let you connect all your ground signals by simply using vias.
4. You should reference the device datasheet for your IC. The manufacturers usually include the physical dimensions of the part, as well as the recommended land pattern.
Trace widths directly depend on the amount of current that they need to be able to hold. There are many calculators online that will help you determine what thickness your traces should be.
5. You can determine your silkscreen width by right clicking on any part of the silkscreen, navigating to "Properties", and then looking at the field titled "Width". Keep in mind that many board houses have a minimum silkscreen width.
Kind Regards,
Willis