#1
do i need to make any adjustments to either my acoustic or electric, if I want to go one down on the gauge?
#2
If you're keeping the same tunings and all, probably not. It won't be too big of a tension change.
Ibanez RGA121 | ESP LTD H-1000
Axe-FX Standard
#3
I went from D'addario 10's to GHS Boomer 9's on my Dean. It was a straight up change with no adjustments. There was a slight change in tone I'm not happy with. The 9's are easier to play, but I'm going back to the 10's when i change again. I keep all my acoustics setup with 11's so I can't help you there.
Dean Icon PZ
Line 6 Variax 700
Dean V-Wing
Dean ML 79 SilverBurst
MXR M 108
H2O Chorus/Echo
Valve Junior (V3 Head/Cab and Combo)
VHT Special 6
Phonic 620 Power Pod PA
Wampler Super Plextortion
Line 6 Pod HD
#5
yes i can
first of all it is a very bad idea to go to 9s in my opinion
tone is lost at 9s and tens are the perfect gauge
but if you think you are then yes especially on your electric it can change the action alot, you should adjust the tremolo if you have one and truss rod or get someone to do it for you

if you feel that the strings are too heavy to bend or something then you just need to practice. one thing to do is use more thatn one finger for the string and that'll help
GT

05 3 tone sunburst deluxe strat
line 6 spyder III 30 watt

epiphone special II les paul
SD-50CE silvertone acoustic electric
#6
i changed from 10's to really light 8's and tuned down to Eb, and eventually my guitar started giving a little buzz, so if you can afford to you might as well have it set up how you want it professionally
Gear:

Stinger Smx
Hondo H-1
Fender Classical
Custom Mini Les Paul
60 watt Mega Tube
GNX4 workstation
6 pack of Shiner Bock