That it won't be easy at first is an understatement.You are right in that it won’t be easy at first but I am sure we will be able to get our own favourable agreements. The EU is bigger, yes, with more clout perhaps, but it is difficult for them to cater for 28(ish) countries. We only have 4 to take into account and as we are so well integrated already, it really is just one country to consider (in most cases).
Not easy, but what price freedom?
The UK doesn't have trade negotiators any more & I don't see David Cameron being too keen to ask Peter Mandleson to work for a Tory government.
The US (as an example) isn't keen to negotiate directly with the UK as was highlighted earlier. Given how contentious the TTIP negotiations have been, an inexperienced team and reluctant partners - I don't see what your optimism is based on other than a hope that it will all work out.