GreyArea:
Is it okay to solder the resistor directly to the hole on the chip (I use pin 8 for data)
Yup. But, try to ween yourself from the term "chip" when referring to an Arduino or Trinket, etc. -- the WS2812B is a chip. The Trinket is a "board" or "module". I had to stumble over your wording a bit before comprehension kicked in 
GreyArea:
is it okay to solder the 1000 microfarad capacitor directly between the +5V and GND holes, or would I be better putting them at the start of the LED strip?
At the start of the first WS2812B strip -- or even further on, like at the junction on the far end of the second strip or even a few caps, at various points along the string (and probably could be smaller value if done that way). But, if it's working fine, then no need to go to such lengths. I mean, long strings of these WS2812Bs function just fine without all the fuss But, the one cap a the beginning of the string is still a good idea.
Also, be sure to connect both the power and the ground of the WS2812B array, to the same point where you connect the power and ground of the Trinket. This is especially important if you are planning on feeding the string directly from the data out on the Trinket, since it will be a 3V signal being fed to a 5V system. By using a 3V signal, noise immunity will suffer. In Fact, I would try it without that resistor in the data line -- the Trinket output is close enough to the beginning of the string, that the chance of reflections [the reason for the series resistor] are nil. And the resistor might reduce the signal amplitude even more. The first WS2812B will boost the signal amplitude so the rest of the WS2812Bs will be driven properly.
GreyArea:
Will these be okay?
Probably, but can't be sure because of the lack of data (as if I could determine anything were the "data" present -- I'm more of a "digital guy" - MCUs and code. Let's just say, it's always worked for me ). I would also include a .1uF cap in parallel.
BTW: I'm used to having access to a nice scope and thus the ability to probe for problems. So, if you don't have a scope, or other way of troubleshooting such a system as you are making [really cool, BTW ], then you'll probably need to over-do things, like adding extra caps and translating the data output from 3V to 5V, use bigger wires for the power lines, etc. merely because it's way harder to refine anything. In other words, forget finesse -- break out the sledge hammers!