Well Jeo by the sounds of it you don't have much "web development" knowledge and you are jumping right in the deep end with a social network platform.
I have been developing from basic html to advanced php / js / sql / blah blah for over 8 years and i have a fair understanding of how to use Oxwall because of my web development knowledge.
I also know that if i need some help that i must provide as much detail as possible, Oxwall support/dev are not mind readers.
Multiple posts and mail from you contain simple "My site broke, please fix" or "Plugin doesn't work it shows blah. HELP!!". This is not going to get any of us anywhere, except put people off helping you.
Oxwall is a piece of software under constant development for free. Addenster is constantly trying to help out around the forums and a few of us try to give you help through our experiences with Oxwall along the road.
I suggest you find tutorials for basic web development and read them as this will help you understand how to setup, manipulate and create web content.
Though Oxwall is an out-of-the-box type of software doesn't mean you can throw a few plugins and you will have a social network ready to battle Facebook and Google+. Oxwall cuts out the basics so you don't need to sit and write code to get basic functions going. It allows you to start using it straight away and produce some great websites.
In response to your bullet points:
1. You shouldn't be releasing your website to the public as soon as you create it, Alpha/Closed BETA/Public BETA/BETA/Site goes live. It is all about finding bugs and developing your website.
2. Why did you have to buy a new domain name, that was your choice.
3. Plugins work fine, if any bugs are discovered they are fixed. Plugins by third parties are not supported by Oxwall but by the developer so that is not Oxwall's fault.
4. I am not sure where you have calculated £300 from, i have spent $50 including a domain name and vps from hostgator. Oxwall costs nothing and the plugins are mostly free except the billing ones and the new IM which totals $110 which is about £70. So if you bought 2 domains at £10 each (max) and shared hosting £20 a month. You have more than likely only spent £100 give or take hosting costs and the plugins you purchased. For a social networking site that is pretty good most software for the platform would cost you 2-5 times as much as that.
This isn't just you either multiple people come on here without naming names and expect to create a facebook/google+ challenger in 30 mins but it doesn't work like that.