Bit of a long read ahead, but the best info can give you as someone in your shoes this time last year.
I've been running the Viv "V3 Billet 6+6 Blade" 19t's for a year / 10k miles now. I already had the 7.5" intercooler, charge pipe, intake cones, catless downpipes, secondary cat delete, and bucketless Walbro 535lph LPFP installed to support a custom ~22psi E50 MHD tune on the stock turbos...I tightened the wastegates once to make it possible, but then a flapper bushing finally broke loose at 110k miles causing a nasty rattle which is why I upgraded to the Viv's. All I bought along with the turbos (all the necessary gaskets for install came with them) were the VRSF Stock-Location 2" Inlets + Outlets, 3gal of coolant, and 7qts of oil + filter. One year later and they're still pulling strong and boost just right, no smoke, rattles, misfires, or any other gremlins.
I daily it on a ~21psi E40 MHD tune by DocVu...given that boost level with 9* of timing by 4k rpm and climbing up to 13* timing by 6500rpm-redline, fuel pressures and ignition operate with ease and pull super strong after 100+ pulls. Last time I dyno'd was under my previous tuner's ~21psi E40 MHD tune, where it put down 533whp / 603wtq on a DynoJet with -4* to -6* timing corrections in every cylinder along with crashing fuel pressure haha. Now with DocVu's tune, it runs way better with a small timing correction that may naturally happen every 1/5 given pulls I do, but otherwise smooth as butter every time with no hiccups felt throughout. This being said, I may see 30-50 more whp if I ever revisit the dyno since it runs a lot healthier. If it helps you reference even better performance potential-wise, my current personal best 60-130mph Dragy Run is a 7.2sec.
Anyway, I'd highly suggest going through DocVu for tuning because the response times are unbelievably great with high consistency each revision. The key is don't floor it until you're past 4k rpm all the time aside from 3rd gear datalogging purposes, and you won't have to worry about the internals breaking prematurely with "all that TT torque." Plus, as others have mentioned, a good tune counts.
Exhaust wise, it'd be ideal if you could at least delete the secondary cats, but otherwise you're good.
I would make sure your ignition coils, spark plugs, and O2 sensors are still in good shape. If you feel like changing out your spark plugs at the most, I have no hiccups on NGK #97968 plugs gapped to 0.018". This is so you avoid pesky hiccups / small misfires. I'm assuming your injectors are in good shape too, but just keep a close eye if you have no record of previous service on them within the last several years.
I didn't see anywhere about you mentioning a LPFP upgrade installed, I can highly vouch for a bucket-less Walbro 535lph LPFP setup, unless you're only limited to a bucketed setup on the 5-Series. Regardless, a Walbro 535lph LPFP is ideal. Easy install, and no issues to this day. This is so your fuel low pressure doesn't crash and starve your HPFP & motor of fuel. A lot of people will start to see their stock LPFP give out as far as an MHD Stage 2+ flash. Speaking of, be prepared to get a new HPFP if your fuel rail pressure can't seem to handle the extra power and constantly dips below 1000psi with misfires. If not, then you have nothing to worry about.
If you ever plan on running more than 20psi of boost, look into the BMS PnP 3.5bar TMap Sensor Kit. It'll be a requirement to properly read & remap the extra boost levels. It's plug-n-play, so no need to worry about anything sophisticated.
The only other important pointer I can give you is to use a hand-pumped vacuum tester and plug its hose into both turbos' wastegate actuator port. If the wastegate flap is closed tight by 6hG, then you're set. If not, you'll need to tighten them. This is so that you don't just slap them on the car to find that you cant make more than 10lbs of boost before your WGDC maxes out.
All this mentioned, as long as your car seems to run fine now and your goal is to be high 400's whp, you can easily achieve that with just a 93oct tune on the 19t's and no trouble hardware-wise. That's nothing on this engine as there are many out there daily-ing a ~700whp setup on full E85 with untouched internals and it lasting for multiple years before cracking a piston / ringland or spinning a rod bearing. Hopefully this helped, keep us updated on how everything goes.
