It will be hard to get visibility with free services and if you are serious then buy a WP Theme (my favorite site is www.prophoto.com it is for photographers but you can tweak a lot and give it a professional look). Yes, adding social sharing features and specially having comments section a must, we wouldn't have been talking if HN didn't provide us this feature, right? I would also suggest that you submit your posts to techcrunch.com www.themuse.com and see if you can contribute in their blogs and get your name out there and then go on your own, good luck!
Absolutely!
It is hard to say as all these companies are the middle man and they charge their base fees and connect you with different skill level people; depends who you get connected with. I've been burned twice so be very careful spending your money. Never put up front money, get stuff in writing, talk to people on the phone and ask for proof that what they already built? See if they measure up to your standards. If money is not issue, go with well known brands/people, if it is then ask the developers for some referrals. This article helps a bit.. http://www.forbes.com/sites/theyec/2014/05/29/the-true-cost-...
Good luck!
Definitely shop around, if you must. Technology is at all time smart and a lot of smart people around the globe so any complex thing can be conquered, just look in the right places. My estimated cost is between $3K to $8K overseas and $3K to $20K in US. This is a great site to start, I think. http://www.toptal.com/
Kudos on the launching the site! You entered into well charted waters but that doesn't mean you don't have room to grow. Try to add features that can differentiate you from Instagram or Pinterest. There are some great suggestions here so don't ignore. Here few things I noticed; the website is cookie cutter WP site, so invest little in design and I think 99designs.com can help. Your site is about photographs and video on homepage threw me off right away as I thought it's video app; and video itself is not related to your product. See https://www.airbnb.com/, how relevant their video message is to their services. Don't get discouraged, pivot!!