All very good advice and all completely redundant.
If you want to build a ship for survivability in Open, you're looking at the wrong ship.
On a similar budget, buy a Python instead.
Alternatively, if money isn't an object, go for one of the big 3.
The amount of sacrifices that you'd have to make, and the credits you'd have to spend, to make a T9 survivable in open would render it almost pointless to fly in the first place.
Course, that's not to say you shouldn't fly a T9 in Open.
Upgrade the shields as much as you can, fit a decent MRP and then "git gud" at high-waking at the first sniff of trouble.
Anything more than that and you'll be reducing the cargo capacity and jump-range to the point where you'd probably be able to deliver more stuff, per hour, in a Python.
A T9 definitely isn't my first choice for Open trading, but the thread is on T9, so I recommended what I could. A Python or Big 3 would have more survival, but it's also off topic as the subject is T9s.
Of course, outside of Open one really only needs decent shielding, with good thrusters and mines if you want to kill hostile NPCs. (Need to be fast enough that the NPC sticks behind you and eats mines)