Solo Bass Range

[basskidd]

So... I just finished (almost, still have to double check everything) a transcription that I've been itching to do for some time, and now comes the time to learn it on bass. There is a slight problem though. The original piece was performed on a Harp-Arch Guitar (a harp guitar with like 10 guitar strings..... ) so I've resigned myself to learning it in a different key.
My question is, how do I decide which key to learn it in? How do I know which key will be good to play it in, but still keep the fret-spacing relatively close (higher up on the neck so I don't have to grow an extra finger or two), make sure I don't run out of range, all that fun stuff...
Anyone have any experience with this sort of thing? It's my first time
Edit: I guess this would also include how to figure out (if any) alternate tuning would work best

Mods - wasn't really sure if this is the right place to post this; if there's a better place feel free to move

 

[FretlessMainly]

One factor is how many strings your bass has, but perhaps most importantly, your top note. Find the highest-pitched note in the piece and compare that to your top note. Then transcribe the piece into a key that allows you to hit that highest note at or near your highest note.

An important thing to consider is that since the piece was composed for harp guitar, the use of open drone strings will likely be useful. So, don't automatically transpose the piece into the key that allows the highest note in the piece to be your highest note, make it so the highest note in the piece puts the piece in a key that lets you use the E, A, or D strings as drones.