If you're planning to use, say, a single 200g surface layer combined with a heavier fabric like a 600/650g, it's most likely that any print-through will be limited to the the resin inlet fitting as the narrower type of resin spiral akin to what EC sell probably won't print through. So, you could indeed try running the spiral across the centre length of the tub mould.

In that scenario, it might be worth installing two vacuum ports, at the centre points either side, but be aware that the resin will likely reach these before wetting out the end sections ensure that resin breaks are used here to slow things down here and allow time for the ends to wet-out. Make sure that you have a narrow strip of mesh running all the way around the edge of your flange to allow any de-gassed air to reach the vacuum lines as things infuse. 

As the plug hole section will be raised, you'd again need to ensure that the bag was sufficiently large to pull down in this area without bridging and creating resin-rich corners around the inlet that will, most likely, be prone to breaking off, especially on a new mould where things will likely be a bit more tough to de-mould cleanly

I'd likely look to cover the plug hole section with small sections of fabric, with relief cuts made in  the main fabric section to slip over the hole. Done neatly, any join lines should be barely visible

If going down the route of placing both inlet and outlet on the flange, though, I'd still avoid picking the corner to corner route, as this looks to be the furthest and could takes ages to wet out fully and make controlling the flow more problematic. Pay attention to pot life and temperature of your resin/mould in all instances as it will impact greatly on the speed at which things infuse.