Advice needed for front setup

Hi

I am building a bike using Soma Double Cross frame.

I am going to use the bike in two setups:
50-36-xx, or 50-34-xx front with 12-23 rear for road use.
(xx = not going to use the smallest chainring)
and
46-34-24 front with 12-27 rear for touring use

In both cases i need a low q-factor.

I have the Shimano Deore LX (FD581) front derailer with the 50.0 mm and
48t max chainwheel capacity and Shimano XT medium cage for derailer.
I have low Shimano 105 STI brifters.

I want to use a 170 mm crank with 5 arm, 110/74 Bolt circle diameter.

That said i have the following questions:
- How easy is it to switch between both the above mentioned setup and
is it possible at all by using the same front derailer only
reseting/adjusting it and swithcing the chainring?

- Is the Front derailer Deore LX right for this purpose. I am worried
about the chainline as on road use i am going to use the outer/middle
chainrings and for touring middle/inner chainrings. I read that Shimano
road (105) STI dont work great with 'mountain' crank and derailers
setup. Should i go for the 105 tripple derailer? Any advice with
respect to the above setup?

thanx in advance
nilay kothari