Modifying Tab

Hi,
I would like to create a plugin to modify the fret positions in tablature staffs for v2.0 (in most cases, based on a notes in a linked clef staff).

I have started going through the plugin development docs/examples.
Below is a suggestion for the code. It would be very helpful if someone could advise if all the properties/methods are supported for v2.0 plugin code.

1. User selects set of notes
2. Specify a user-defined variable for each note to represent the neck position (e.g. 5th position). e.g. by typing this number into a modal/modeless dialog box.
(Is there already an appropriate note variable property I could use for this, or is there an unused "generic" note property (integer) I can use to store this?)
3. Read string tunings values for each string.
4. For each note value, calculate the appropriate fret (the math I can do)
5. Modify existing tab string/fret values in tablature staff.
(6. As an option, also add the position as Roman numeral above clef staff)

Also, could someone suggest a good plugin example with a modeless dialog box, with a (numeric) entry field and a button for "update", i.e. run some code (it would be nice to have this box floating around, select each set of notes, choose a value, and update, as opposed to running the plugin each time...)

Many thanks for any help,
MT