Allegro Semi

I am writing a concerto for cello, and I'm stuck when it comes to writing pieces for two instruments ...

This is the bassoon (like British Columbia, but with a bit of a "Concertino" party, where he Echos cello).'m Wondering how difficult it is to play semi-quavers (the allegro movement) in the upper register ... so there fingering / combinations of notes, which are really difficult.

In the accompaniment, there is a section where I have a cello "doubling" as archlute. (I have a guitar and cello, which plays the role of lute because nobody archlute Wounds, and some notes were too low for the guitar). Perhaps playing the cello "guitara pizzicato almost"?

Thank you

Yes, the cello can be played pizzicato almost guitara, but it depends what you mean, I assume you mean to pick the bridge. There is also scratching through all the strings like a guitar. (Note: the note should be playable in triple or quadruple scores arrested for this purpose).
A guitar can be recalibrated to obtain tickets at low, but beyond the third string is soft ..
The upper register (above f c above center) is difficult to play the melody or hard on the bassoon. Here is easier, but not a high range (up one). Saute would add difficulty, and tonguing is a factor. Scale legato easier to be wise. It depends on the player's skill.
The bassoon is the hardest instrument to play in harmony, in general, since the application of valves has been done here in success. Thus, in a student orchestra there is less likelihood of good performance in a professional setting, in a greater degree than other instruments.
Walter Piston book on orchestration gives the fingering positions for all notes of wind instruments, are also tabulated in the textbooks for the instruments themselves. The verification of these and other sources will give you clues as to its ease of implementation.
Just a quick word here, good luck with your business, all the best for you. Just an info, I am writing for an orchestra-level students as much as possible. Purposes: one is more likely to earn a return and such performance is likely to be better if the parties are easier. So, I do weird instruments and virtuosity. Although when I started, I wrote my share of bassethorns and tubas Wagner, did I mention tenoroons? Just my take to improve the chances of our task difficult.
But again, follow your dream. This is what they are for.
Edit; Run Part bassoon bassoonist your past, the method is that Strauss and Wagner used to push the limits of orchestral (with some funny stuff between Wagner and Tombo harpist)
Again, what you say, the cello can play chords Lake strumming a guitar. This is usually done with a finger (if a plectrum can be specified), it is usually done with a fast, either up or down. The normal is to pick the lowest note of, if the opposite is needed, an arrow pointing downwards is placed before the agreement.
With a quick agreement, it must be fingers on the cello as a convenient stop triple or quadruple. The Berlioz / Strauss orchestration Treaty lists the possible agreements, other sources speak generally fingering questions and suggest intervals.
The most successful agreements have the most open strings, also the highest on the easier they become, as the fingering is similar to the hand. The thumb adds an additional resource when you reach senior positions.
Those arrested multiple strings of the cello is much more difficult than for the viola and violin, because of the size of the cello and the tension on the strings. It is almost impossible to find, even for low and usually a string is in question. To control the use of them, i.