Fast Track Layout

The most common suggestion for a new layout is to go with the largest diameter curves your space will allow, especially on your mainline and anywhere you might want to run a larger Locomotive.  Some have minimum curve specs from 54 to 72 inches.  If you were to modify your plan from a horseshoe to be more of a C where the opening is about 28" you could build a hinged bridge across the mouth of the opening.  This would allow you to use 0-72 curves or greater in an oval shape.  With the space you have you may also want to consider a double main line.

If you stay with your current base plan, be sure that you maintain access to all sides of each 4x8 base.  If you place track at the back of a 4 foot wide piece of lumber, Murphy's law guarantees that every derailment will occur back there, forcing you to climb on the table to fix it.

Chuck

Also get a good transformer that has enough power for your mainlines and your lighting, accessories etc.  go with either a Lionel, ZW with two 180 watt bricks, where you can add on extra two bricks or a MTH Z 4000.

If you have 14' wide this will provide for larger diameter curves than 4' sheets - this is 3 sheets cut up

Oops , I cut 1 full sheet that didn't need to cut

You get the idea - now you can use 048 curves

Not sure what your goals/intentions are, but here are two thoughts:

First, one of the strengths of Fastrack is that it is the most repositionable track system.  You don't have to take advantage of that feature, but it is very easy to simply play around with different Fastrack layouts.

Also, the 36" curve is indeed the largest Fastrack curve that will fit in 48".  This appears to me to be a design "sweet spot" for Fastrack is the sense that Lionel offers Fastrack switches up to 36" in a non-wired/non-motorized configuration for the 4x8 user (also considerably cheaper).  As you move away from this, some of the advantages of Fastrack over other systems start to disappear.

Here's what O36 (gold) looks like compared to O48 (blue). Like others have said, O36 is the largest that will fit unless you can add to the sides. Then the reach becomes even longer unless the space is open on all 4 sides.

Here is a rough idea of what I meant by "C shape layout with double mainline O72 curves in a 8" x 16" space.  The reach in I used here is 30" from the inside, but you can make that how ever far you can reach over your scenery.  This is obviously a very simple design that you would probably want to add more track features like a reversing loop(s), sidings, etc, but just trying to give you an idea how wider curves could be used in your available space.

Solder 14ga feeder wires directly to the tabs underneath the fastrack  at least every 10' of track length.

My layout is 16 years old and I've never had a voltage drop issue. IMO you get a much better connection than trying to use slipon connectors. Should you need to make a change a few seconds with a hot soldering iron releases the wire.

You don't need an expensive soldering iron either. I use a simple 25w Weller iron. Works just fine for this.