I would say it is a "beautiful pair of shoes". This is because the "pair of shoes" is the noun. When talking about shoes, in English, we talk normally talk about shoes being in pairs. "Beautiful" is the adjective describing the noun, so it would be a "beautiful pair of shoes". However, a more natural answer would be to just say "beautiful shoes" as it is assumed that they are a pair. Hope this is clear

I would choose the answer based upon which demonstrative is(/will) being used, "These are a pair of beautiful shoes " or "Those are a beautiful pair of shoes". Scenario 1) if I possess the shoes then "These...", if I want to possess them then "Those..." 2) proximity.. if the shoes are nearby then "These..." if the shoes are far away then "Those..." Hope that helps, Rob