Get selected file size and path in Lightroom (tested with https://github.com/nitoyon/lua-console-lightroom-plugin & Lightroom 4.3)

test.lua

local LrApplication = import 'LrApplication'
local catalog = LrApplication.activeCatalog()

local size = 0
local pathes = ""
local photos = catalog:getMultipleSelectedOrAllPhotos()
for k,photo in ipairs(photos) do
    size = size + photo:getRawMetadata("fileSize")
    pathes = pathes .. "\n" .. photo:getRawMetadata("path")
end

return string.format("%.1f MB%s", size / 1024 / 1024, pathes)