I have played with a proxy toshiro and I think he does well with buffing the ashigaru. He helps get them going with his teki o jüden action. I didn't seem to get there plus from being near him to often cause he would move elsewhere to help my line.
I also was able to return a ashigaru using his eternal servitude, but I got lucky having a 10 :crows in my hand to cheat. I was up against avatar Sonia so it didn't help much but it could elsewhere.
The soul porter I think is a must because of his empower ancestor action. If I didn't use link and that to move toshiro up he wouldn't be able to keep up to the ashigaru. Plus being able to have a little wiggle room to grab up his relic if tosh eats it.
I don't think you need to sleeve the retro deck. I personally dont like sleeves much anyway. But I found that if you take a tea light candle and rub it on both sides of the cards you will almost solve the slipperiness problem until you wear them down in use