Model Railroading > O-scale, Lionel, MTH, Atlas, K-Line, layout equipment questions

Hi everyone,

No shots just observations:

Are there a good number of members here who have O-scale (not necessarily scale but more in the Lionel realm), on this board? Seems like blasphemy as the preponderance of content here is of the HO variety but still..

Got a lot of questions now, considering I added O-scale Lionel and what-have-you to my collection as of November of 2021.  Plan is to have Lionel running overhead with a 1-2 deck HO layout below.  Lionel is being suspended from the top of the wall (railhead is approximately 12 inches from the ceiling on shelving on one side, with suspension for the other side).  Will post iphone pics soon of the current train room mess with all the included disorganization lol to give an idea of the plans.  Its an around the walls plan, with 2 back-to-back wyes to crossover in the center of the room.  This is all overhead, with at best 72 in clearance under it to the floor.  I'm doing large radius curves (O-72-36in rad, O-84-42in rad, and O-96-48in rad) to accommadate the biggest engines I've now got-2 B&O EM-1s.  I'm including a graded line to start in part of the layout to go down, around and dive under the upper line on 3-4% grades.  Has anyone done this anywhere?  I've been told that Lionel engines will be fine with this grade, unless I do Atlas track, which I'm not.  I made expensive rookie mistakes and had all my track bought as Lionel Fastrack until I heard how noisy and loud it is and went looking around again.  I found GarGraves and Ross and went that way now.  My Lionel engines (the vast majority of my collection) have Magna-tracton or some derivative (including traction tires) so I'm sure they will do fine on the more realistic looking track.  I'm using 1/2in birch plywood throughout, with 1/2in homasote on top of the plywood, then 2 stacked pieces of cork then the track for my roadbed.  So I've worked that thickness out to about 1-3/4" from railhead to underside of the plywood.

My questions are this:
-Can I reasonably expect L-girders made of 1x3 to support spans of 8 ft without too much waves from train movement?  Especially large stuff like Lionel?  
I'm going to need those spans to keep the overhead as clear as possible on the center crossover line.  If I go larger (1x4), I may be hitting my head a lot or always being hunched over (I'm 6 ft tall).
-What wiring connections would be suggested to add some sort of modularity to the design?
I'm looking to do this work and not have to lose it again if we move again.
This includes gusseting the joints of the rodbead and accounting for that on some of the supports

I know I went very wordy here, but I am looking to start this conversation and tap the wealth of knowledge on this board.  Looking for tips, ideas, and yes truthful ideas and opinions, even ones that are what-the-you-know-what.

Thanks again y'all,

B&Oblades
aka Jason

I have four mezzanine "layouts" at my house. One is on my patio, two in my garage (double deck), and another in my computure room. They are basically loops so I used Gargraves track to accommodate "O' gauge 2 rail and 3 rail easily. I can run trains in three different are in the house! My patio layout is "G" gauge and one more "G" layout in the Garage! Never a dull moment!