How do I go about launching a seed round?

From my experience there are different ways to do that based on the type of ur product/service, stage of development, the metrics you achieved so far, and ur location. you need to build a network of connections. find entrepreneurship meetups and events .. go network. look for events and conferences where you can pitch your ideas like this one http://nyc.thegmic.com

A good option also is to apply for one of the accelerator programs that can provide you with support, mentorship, networking opportunities, and seed fund like YCombinator and Techstars. Check GAN accelerator network. Have a look also at crowdfunding websites like kickstarter. the cost will differ based on the way you choose but i recommend not to worry now about the legal/tax issues nor the cost but worry more about metrics that matter to investors like acquiring more customers, cost of acquisition, retention rate, growth rate, etc. and raising fund to keep you going.