congrats on your upcoming twins pg
it sounds like you have got a good support network around you to start with which is awesome
i would suggest getting a feeding pillow
i used one when feeding my twins, but it was hard to balance them both sometimes when they were really small as they were different sizes- there is definately a knack to it, but the fact that you have breastfed before makes it so much easier!!
the best bit advice i have is to join your local mulitple birth group. not only are they a great support group, they often have a second hand classified, cheap breastpump hire and will be in touch with what are the latests and greatest pillows and other products available out there. once you join you are also entilited to some discounts when you show your card to many places!
if you go to AMBA's main website they have a local club finder as well as heaps of other good information and resources on line
as for feeding in public, there are several ways that worked for me- i either expressed beforehand and bottlefed them that feed, fed one at a time, or took a feeding pillow with me and fed them wherever i was. Unfortuantely with 2 babies at a time, the ability to just pop out, or just duck out somewhere goes out the window. Even just ducking to the shops means getting the pram out, getting the nappy bag out blah blah blah
so taking a feeding pillow with you is no biggie- sounds worse than it is lol

getting your supply up? your supply should hopefully just keep up with what your babies need i was expressing up to 2 1/2 litres a day with my twins. when i needed to get more, i upped my water, and i took blessed thistle tablets . Fenugreek tablets are also suppose to be good and there are always those lactation cookies to try as well!!
it is definately alot harder with twins- i didnt realise how much more work and how much harder it was until i had a singleton. but you do it and it is awesome! you are never given more than you can handle i say!!!
good luck and if there is anything else you need to know- just holla