I think that DME is easier to work with than LME. With LME, you have to make sure it's all mixed in, it sits on the bottom until it's stirred in. With DME, you know when it's stirred in properly, there won't be a bunch of clumps.
As for the Irish moss, don't worry about it. It's for clearing. It's possible it would take a little longer to clear, but I haven't had any issues with forgetting it.