Kakes

I'm also considering how to make bases for tables, though will use wood not glass.  One of my teachers just made a couple of furniture pieces that are gorgeous.  You might look at the work of Austin Coudriet or Kelsie Rudolph (both are on instagram).  Kelsie makes handbuilt furniture and Coudriet large-scale sculpture and furniture.  He has great tips about drying and firing large work.  Rather than using steel rod I think you might want to consider building internal support structure (out of clay) that prevents slumping and provides strength.  Both these artists show useful examples of this construction and it's been helpful to me.  

Mostly things to change the viscosity for brushing and some flux to make the slip adhere better to the greenware underneath after firing.

That is pretty close in rates I doubt it will matter. As with everything though, best to test before you commit to a ton of production work.
I make a slip out of a clay body that I dry and then grind down into a powder form so I can mix it with other additives. All of my work uses this slip over another clay body.
I love slipping pots this way, it adds a lot to the final form if done right. I am not sure exactly what you are after, but the best thing to do is try applying you slip to different stages of the green ware in the drying process. Find which one you get the best results with for what you are after, and then repeat that process a few times before committing it it.

Truth be told Kakes you are exactly a "typical ceramic artist".  No need to apologize. The major ceramic companies, Duncan and Amaco, designed their product lines to serve customers just like you. The ceramic choices at 06-04 are much more diverse than the choices at cone 6/10.
I work with a number of young people, recent ceramic grads, who are not concerned with durability or process but instead with simply making "interesting/unique" ceramic objects. I applaud their ambition as I applaud yours. 
Your results may not be, exactly what you want them to be, but if you lower your expectations a notch you will find some amazing results nonetheless.

All very good reasons to work with low fire clay!

This is something I find really frustrating about ceramics. I come from a background in painting, so it's been a major shift in working methods and especially my attitude towards these technical demands. It's overwhelming at times. I realize there's no shortcut. Sorry, just venting. I do appreciate the technical expertise offered here and have learned some very important tips that have made a huge difference!

I'm not so sure it would. For testing MOR a three point support system holds the sample piece while pressure is applied in the middle of the sample until the sample breaks. (I simplified the process) In real life this isn't what happens. We bang or drop a piece and it chips or cracks. Lots of variables as have already been mentioned plus there are factors such as sintered vs vitrified, clay density, particle size etc. If you have concerns then look into which couriers cover breakage plus what the cost and coverage is. There are many articles online about how to best pack ceramics for shipping.

Hey Kakes,
The first thing to mention is your terminology.  Typically stoneware clay is not considered "low-fire". It used to be considered "high-fire" (fired to cone 10) but more recently many bodies have been mixed to vitrify at a "mid-fire" temperature. (cone 6) 
Earthenware clay is more typically considered "low-fire". ( fired to cone 06) The two local companies, Minnesota Clay and Continental Clay, both sell earthenware clay but I know several potters who like to fire their earthenware pots to cone 2.
In a sense any vitrified clay is highly durable. In my experience, however, earthenware tends to be a bit more brittle than stoneware or porcelain clay, after firing.
As to which is best, that, I think, would be more about color range you want to work with. If you're finishing the pieces in glaze earthenware temps give you brighter colors and a broader color range.
Hope this helps?
 

If you’re concerned about the fragility of a sculpture as opposed to a pot, how the piece is constructed is going to have more of a bearing on the durability than the clay body. A thin walled piece constructed with the best methods described in Min’s link above will still break sooner than a brick made using the exact opposite principles. If your sculptures are thin walled and unglazed, making them out of earthenware glazed with a well fitted glaze will add strength, but you’ll still need a lot of packing padding. If your pieces are solid, they’ll withstand more impact. But even construction bricks break if they’re dropped from enough height.

If it's an indoor sculpture, any clay body is strong enough regardless off the firing temp. How you pack it is much more important. In terms of deciding how hot to fire, that will depend on what types of surfaces you're after, and what materials are needed to achieve that. You'll also need to consider the shape of the piece and how the clay will respond to different firing temps. Porcelain is more likely to warp and sag when fired to maturity, low fire temps won't have that problem.

Pete Pinnell did a test of claybody types many years back and one of the things they tested for was modulus of rupture, don't know how relevant that would be to your question although it's an interesting read. Link here to it. I would hazard a guess that how you pack and ship your sculptures might be more germain.  
Sorry your question didn't elicit any responses in the chem section.

I believe earthenware is very good for sculpture. Yes, you can use glossy glazes and bright underglazes. They’ll stay bright and colorful because of the lower firing temperature. 
It will not be as strong as stoneware or porcelain fired to maturity, but that doesn’t mean it’s not strong.
Earthenware is usually only fired to bisque temperatures and is generally stronger than bisque fired stoneware. Taken just a cone or two hotter, some earthenware develops significantly higher strength.
Those 8000 terra cotta warriors are still around, I say earthenware for sculpture is a go.