Eagle Cad – redefining terminals of a component

What do you mean by 'standard'? Resistors with different power ratings have different standard sizes (for example, 1/8W vs 1/4W). Likewise for capacitors, the part you need to use depends on the type of capacitor (monolithic, ceramic, electrolytic, etc) and the capacitance and voltage ratings. Assuming you are looking at the RCL library, 0207/10 simply means the body of the resistor is 2mm x 7mm and the hole to hole spacing is 10mm. Similarly C050-035x075 means 5mm hole spacing, 3.5mm x 7.5mm outline. You have to figure out (with calipers, for example) if this will work with the parts you are planning to use.

One thing you can do is print the board layout at 1:1 scale on paper before sending it out to the fab to see if the parts fit. You can catch common errors this way.

As @mattyoung suggests, you want to panelize. Eagle doesn't panelize. However there is an incredible piece of software which panelizes gerber files fantastically well. It's called gerbmerge, and it's free. It runs on Windows and Linux (and OSX, and anything that can run unixy code).

I highly recommend it for this kind of work.