Since you have a bunch of different stuff on hand to choose from, there is no need to use other stuff, thats a great thing!!
It seems the decision is how to define what will work best... The VHOs and grow lights and the light will work and the MH will work, the grow lights will work. For plants you want a color spectrum around 6500k or so (all have that), I would set up the MH as a single bulb (but I like MH and use it for everything, but I also have a chiller and dont worry about added heat).
It one comes down to a preference issue (heat, higher PAR, and possibly higher operating cost for MH vs. lower heat, lower PAR, and lower operating cost for VHOs), I think its probably a tossup.
On chaeto, if it gets proper lighting and is growing you can put it wher you want, flow would be good where you are talking about. I dont remember off hand, do you have a light on your sump? If no, I wouldnt do it, if yes, try it out!
IME, skimmer ratings are arbitrary, as the bioload of every tank is different and when it comes right down to it, Im not sure anyone can define 'lightly stocked' or 'heavily stocked'. That being said, getting a skimmer that is drastically different, high or low, probably isnt a good idea either. I would get a skimmer rated anywhere in the range of 100-300. Im not directly familar with the skimmer you mention, but most of the mid-high range brands to a more than adequate job.
The is coming along really nicely! How is the plumbing coming? Did you get my email?
The MH bulb will work nicely for your fuge, its going to grow all kinds of great stuff!
The Eheim pump is a great Christmas present, that is a really excellent pump, I know that you will be happy with it. I calculate head loss using this website, http://www.pondarama.com/html/friction_loss_charts.html and the pump curves from the manufacturer. It is all additive, so you take the height from the manufacturers curve, and add the horizontal distance and fittings from the other website.
I still need to do some research on your goby question, but I havent forgotten!! It has been a pretty crazy couple of weeks!! I have a huge push of work for a major project that we have been working on and a lot of my folks are pushing to itt done so they can go on vacation in the next month or so.
Did you guys end up getting a bunch of snow too? Its crazy, DC is still digging out!
I posted a response on your other thread the quick version, though, is yes, there is a reaction, soak and dry out the rock OR use a strong dechlorinator and chlorine test to verify your good, use your safety equipment, follow the directions on the MA, (I think its 3 or 4 water to one acid but PLEASE double check me), look up right before you do it which direction to pour (I always look this up before I do it), just let it soak a few hours then remove, rinse and let dry.