I think you may be 'expecting a lot' from a 1195# trailer, unless you go all 'foamie' construction. Using 'standard' TD construction methods (1/2 or 3/4" ply walls, or 'stick' type wall construction) the weight starts to add up pretty fast. Remember, that 1195# includes the trailer weight too, & often a little bit of 'gear/supplies' adds considerable weight.
I'd definitely do the tongue extension but I'd use a 2x2x3/16" square tube starting at 2nd cross member from the front. I'd also use 1.5x1.5" (minimum, 2x2" even better) steel angle bolted between 1st & 2nd cross members underneath, & bolt the tongue extension between them rather than do any welding. Turn your coupler base upside down to contain the tongue extension & go with an aftermarket coupler that fits the extension. That's how I did mine & the only thing I'd change is I wouldn't drill vertically thru the coupler base/tongue ext; I'd just let the coupler base provide any needed stability.
You may or may not need to move the axle back, depending on how you fit a 5x8' cabin on the chassis. If you plan for sure on having a 'receiver' at rear for a bike rack or whatever, I'd move the axle back a few (4 or 5) inches. I dunno 'bout 'reversing' the axle to move it back; first I've heard of that??
I've found that the BAL type crank down stabilizer jacks work very well & are generally easier to mount than scissor type jacks, JMO
Instead of welding the 'A' frame members I just replaced the removable pins with bolts/nylok nuts & called it good. The only welding I did on my 1740# HF chassis was adding the tabs for the front stabilizer jacks. Near 7yrs, 20K miles & one rear end collision later everything is holding up well & nothing has 'shaken loose' yet
Check my album for lotsa pix before, during, & after construction...
Oh yeah, I don't think I'd remove any spring leaves. You'll probably need all the capacity you have.