firstly you dont need thousands of pounds, although a few hundred would help
what is needed is lots and lots of committed people, to get those people you need to establish consesnsus that this is a good idea and that it is worth devoting energy to
urban might be a good place to try and establish that, although general might call up more and divergent support then dusty old p&p, im interested, im sure others would be
it enough folk show an interest than a meeting needs to be called, probably a closed meeting of those concerned followed by a widely advertised open meeting
if consensus is agreed at the meeting to go ahead and various conditions agreed on eg co-operation/non cooperation with police, sectarian/non sectarian, single issue or broader etc then may be the time to talk to larger groups like liberty or no2id as well as smaller groups who can all agree to work around the frameworks agreed
if its a popular idea then the network will grow, ideas will spark off a plan will form itself
next stept pick a date and announce it as pubically as possible
then wed be committed, all we have to do then is organise puyblicity, stewards, speakers, entertainment, dealing with cops, legal support, press, transport, medics yadda yadda
believe me though thats the easy part