I'm still in the process of setting up the tracks on my HO layout. I am setting up my layout to have my bench work as a two level bench work layout that runs completely around the inside walls of an old recycled 20 foot travel trailer except it doubles back in a 180 degree turnaround on each side of the entrance door to give a complete (in a roundabout way) continuous circular run that goes between the lower level and the upper level..

should I lay out my buildings first and then lay track accordlingly

I started installing my drop ceiling, and will be figuring out locations for the recessed lighting fixtures soon. The top deck is about about 30" from the ceiling and will be lit using recessed lights in the ceiling. The lower decks will be lit by LED strips under the deck above. The upper deck is roughly 24" deep. My question is, where is the best place to locate the recessed fixtures in relation to the benchwork edge? I was experimenting a bit, and if the light is too far in the aisle, then I get a big head shadow on the deck.

I didn't pay close enough attention to the exact location of my furnace and now my planned helix is going to be a bit tighter than I thought. I have the inside track at a 29" radius and am wondering if maybe I could knock that down to 26 1/2".  This is in HO.  I currently have 2 1/2" spacing on the helix tracks.  I am modeling 1975, so there are TOFC trains which will likely be the longest cars.  What do you think? I'd like to shrink the helix size down a bit, what would you say is the minimum reliable radius?