Re contrabassoon, here's a quick answer: your instinct is good. :-) Almost everything is more difficult on a contrabassoon. A contrabassoon is similar to a bassoon, but they are more different from each other than, say, a piccolo is from a flute, or an English horn is from an oboe.
The fingerings are, with one exception, superficially the same as for a bassoon for the octave and a half from the lowest Bb up until "open" F (written F fourth line bass clef). The exception is the Eb below open F, which uses an extra key instead of a fork fingering to produce the Eb.
That said, there are certain things that can be easier, or harder, on a contrabassoon than on a bassoon. For example, the Ab/Bb trill is problematic on the bassoon, but much easier on a contrabassoon. Another example in the other direction: virtually every modern bassoon has an F# trill key for E/F# and F/F# trills (around "open" F), and many modern bassoons have an F/G trill key; but the F# trill key is a relatively uncommon option on contrabassoons, and I've never seen a G trill key on one.
Once the contrabassoon goes into the next octave, all bets are off. Depending on the note (or trill) in question, fingerings can be similar to or different from the bassoon. For example, the fingerings for the Eb, E, and F above middle C are completely different from the bassoon. For that matter, fingerings can be different from one instrument to the next, or from one reed to the next, or from one player to the next.
In addition, there are new versions of the contrabassoon that have their own fingering systems that can differ substantially from the not-so-standard "standard" contrabassoon. The differences generally manifest themselves in the higher registers of the contra, improving them in certain cases dramatically. One example of this is the Fast-system Fox contrabassoon. There are a few others.
Finally, there are ranges of the contra that are known to be problematic. For example, the notes around written middle C to Eb are known to be weak and out of tune. There are ways around these limitations, and it's our job as players to make such passages in music work, but it's good as a composer to be aware of them, and write accordingly.
The high range of the instrument is weak compared to the bassoon. You want to be careful about writing a high tessitura for the contra, unless you know the player can play well up there, or unless you're striving for a particular effect.
Again, some of the new developments in the contra have addressed these issues, more or less.
I hope this message was more helpful than confusing.