Varicolour symbols aren't perfect and usually used only for a bit of variety, so they might well be not as heavily shaded in some situations as the regular non-varicolour symbols. The situation with building entities is similar. They are used mainly as infill in large cities and don't always perfectly match the regular symbols.

There's also a mismatch in the scaling of the symbols and the roof fills used on the buildings, in that the buildings are twice the default size, having been pasted at a symbol scale of 2 rather than 1. That's not a problem in itself, but it does mean that all the tiles on the buildings you draw will look only about half the size of the tiles on the symbol roofs. The solution to that part of the problem is to double the scale on all the roof textures in the Fill Styles dialog.

In this shot I have rescaled the appropriate roof texture and drawn a new building in the "SS5C Rounded Shingles Grey..." style. I've also used different sheet effects to the ones you had set up - switching the existing set to inactive and copying across the shadow effect from the SYMBOLS sheet.

The beauty of sheet effects on the BUILDINGS sheet is that you can add colour altering sheet effects and the buildings will respond. I've added an Adjust Hue/Saturation sheet effect to make the buildings paler.

Here is the setup I used if you want it. Only that one roof texture has been rescaled from 40' to 80'. The rest have yet to be done.

EDIT: sorry, for some reason I accidentally deleted the very first paragraph before I posted it the first time. It's back now.

No. This one was uploaded about an hour ago.

Ralf has kindly uploaded an update to the style with bug fixes and an improved set of templates. You should be able to redownload and install it over the top of the old version from your registration page.

I recommend doing that before you start any new maps.

Connecting symbols with actual corner pieces have never worked in metric maps. This may change at some point in the future, but that is just the way it is for now.

Connecting symbols that have no actual corner pieces, like a fence or a hedge where the pieces are all straight sections, will work in metric templates as long as you use the set that has 'metric' in the symbol name.

Yes, you could make the map as an imperial map; sizing the map to be the same area as the metric map. Draw the drains using the connecting drain symbol in the imperial map, and then copy paste the resulting drains into your metric map. I'm not sure if you would have to scale them down during pasting, but the pattern and width of the drains would be correct.

One more thing - the corners or bends are done in 15 degree steps, so you may have to slightly modify your layout if you want to be able to connect everything smoothly.

Looking at lots of other OPD contest entries here (beware the results that aren't valid OPD entries), It looks like at least half the page is text, so the map would have to be really tiny. It might also be easier to do the map part in CC3, but then export it as an image to paste into a suitable word processor (or desktop publishing app if you have one), to add the blocks of text.

It is very much up to you what style you chose to use, though I would recommend you chose one that is pleasing to you to look at, and which has all the textures and symbols you will need.