How long since it was finished, how did you know it was finished and is it fully carbonated yet? Sometimes a few weeks conditioning can make profound differences to the flavour and mouthfeel characteristics.
IMO weak and watery is not that likely to be an issue resulting from choice of S-04 itself, making a starter may not make that much of a difference however that gear should be helpful but more for propagating liquid strains and particular circumstances. Underpitching (not enough and poorly- handled yeast) would be a possible issue and sometimes its a big rookie pitfall, usually manifests itself in sluggish ferment, strange and undesirable flavours, but its hard to say without more info. Some details on your ferment temperature control and details about the brewing process would help us.
Are you sure you want to try the same FWK, if so can you get some specs on it? Some of the retail FWKs aren't real flash when made as bog standard, they often scream out for extra hops or a particular yeast, but Irish Red isn't really a style that this would be applicable to. Other AHBers may provide their views on your particular FWK as well, does the retailer have any advice?
Anyway, there's a few things to contemplate, HTH.
Oh, and welcome back! Yes, hasn't the homebrew landscape changed radically over the last decade, there's been complete upheaval mainly around equipment, range of ingredients- there's a much stronger homebrew scene and vast craft brewing movement.