Here is what I have to offer, these are my comments based on my real world and hands on experience with these cars over 30 years. No, it's not gospel, it's just what I have observed and personally experienced, many others may have a different view point or opinion, your mileage may vary.
As far as your questions about shaft play on your turbo, if it has so very little side to side movement, and there is no evidence of the compressor/cold wheel touching the housing, it's probably just fine and could last a long time especially if you keep your oil changed, the oil and water lines remain in good condition and you don't run it hard and then shut it off almost immediately. The life of your turbo for the most part is a matter of keeping clean oil in the engine and giving the turbo a chance to cool down at least a little after some spirited driving and before you shut it off. One of the best things you can do is to add an in-line oil filter to the turbo oil line and that will require you to get a stainless steel braided replacement line, I like the larger diameter ones available from Chris at turbos unleashed.
As far as making more power, you sure have a lot of options when it comes to modifications. I have built several turbo Dodge engines in the past. I mean I have spent tens of thousands of dollars building them and several of them had everything you could get, forged this, ported that, bigger other, you name it. And it was a lot of fun and effort to get those engines well tuned so that all that expensive stuff actually gave me more horsepower. These days, I put modifications into two general categories, those that make the engine stronger and more durable, and those that will help make more power IF the tune is also upgraded.
So here is my general advice, if you are not going to accept on the front end that if you go with a ported head, ported intake and exhaust, and maybe a bigger turbo and then injectors and an adjustable fuel pressure regulator and bigger exhaust or any combination of the above, you are going to NEED to get a custom calibration to bring it all back together and make the power you were hoping to obtain, then forget it and save thousands in busted parts and time. If you change ANYTHING in the intake or exhaust or head that results in a measurable increase in air flow, your calibration will need to be changed to make the most of it. And if you don't then you are going to have some type of high-boost air/Fuel (A/F) issue that will need to be corrected or you will toast the engine eventually and that is just a given. You can spend quickly and easily $2K-$3K or $4K on all the stuff I mentioned and more and w/o the proper tuning (and a clutch/tranny combo that can handle it) it won't be any faster or will be slower and less reliable than if you just left it all entirely stock except for a heavier duty clutch and just went with a stage 5 ECU, +40 injectors, a 2.5" exhaust, and an adjustable fuel pressure regulator, all capped off with a wide band controller so you can get it dialed in.
The factory equipment, as is, is more than capable of making 200+ HP with a stage 5 calibration, probably even a stage 3, and those setups have already been dialed in and the components all work together to deliver a smooth idle, great daily driveability, good fuel economy and reliability. It's stock appearing for the most part, the pieces are widely available and not exotic and can easily be worked on. ARP fasteners are a luxury, if you are not running 20+ PSI, ARP head studs or bolts are a waste of cash...but a nice to have. They fall in the category of nice to have makes the engine stronger. I personally think it's better to just have new quality head bolts and a good quality head gasket and a flat deck and head to put it on. ARP rod bolts are a nice to have, makes them stronger but frankly the factory bolts are designed to take more abuse than the engine will deliver with the factory parts and up to 15-20 psi. Same goes for the main bearing bolts, they are fine till and maybe even if you are running 20+psi, they are a nice to have but not absolutely necessary. Our engines just don't commonly suffer from rod or main bearing bolt failures. They are prone to blowing head gaskets if the bolts are cheap, or the head gaskets cheap and/or old or the engine is run hot a few times.
If I just wanted a bad arse street machine I would save at least $2000 and just go with a stage 5 ECU, a 2.5" exhaust, an AFPR, and +40s and skip the $1500 ported head, the couple hundred on the ported intake and exhaust manifolds, the larger throttle body, the fresh air or K&N cone filter, the obnoxious BOV, S3 cam, adjustable cam gear, the POS MSD ignition that wan't designed for our ignitions anyway, and all the ARP fasteners except maybe the head studs because if the head does come off it saves me about $40 not having to replace the head bolts every time. I don't believe in reusing the factory head bolts, or the FelPros and I don't give a dang who tells me that they have reused theirs numerous times w/o a problem.
A stage 5 setup, with all factory hardware, add the Bee-hive spring update, PT lifter update, ARP head studs, and if I decided I wanted it to take a regular beating I would add only forged pistons from either Wiseco or Venolia and crown it with meth injection, a progressive meth system if I wanted to add a few hundred to the build. Believe me, that is more than enough for the daily driven street machine and would also make for an awesome every other weekend strip ride that you could drive to and home from the track.
If I wanted to build an engine and tranny that I was going to race regularly and hard, I'd go for all that other stuff, ported everything, a bigger turbo and large FMIC, 3" exhaust, and all the other stuff needed for the stage 5 cal, ARP fasteners everywhere, forged pistons and crank (even though it is like 12+ lbs heavier) and the strongest tranny like an A555 or A568 with a Quaife LSD, and a wide band and learn how to burn my on calibrations so that I could give it a genuine good tune.
I could have literally bought at least two other daily drivers with all the cash I spent on all the go fast goodies for my street machine and would have probably been happier and saved a lot of time (and ca$h) had I just gone mostly stock with a stage 5 calibration and the few select pieces needed to go with it.
Just my thoughts, others may differ, your mileage may vary.