I would just get the cartridge, it should be refurbished with rew seals etc - it should come with some sort of a guarantee, you have 60 days to leave FB etc, if you pay by credit card you could get a refund through that etc
Youre old turbo is "totalled" with the shaft sheared/ siezed, its a specialist job to rebuild it, if your new cartrige is a "refurb" they may want and old one for exchange, watch out as they may reject your old one in that condition and you may have to pay full price (no "exchange subsidy") depending on seller
thea turbo would not have been making any boost whatsoever and it would have been like a (low powerd) NA car - i would be surprized if it pulled over 40mph!
Glad you "took the plunge" and much respect!
The oil feed pipe comes from the pump and the return goes back to the sump, obviously you dont start the engine with these disconnected and the pipes cannot be reversed, you can drip some fresh/ clean oil into the bearing on rebild so it does not spin up dry when you 1st start it
the turbo blades are delicate, dirt can get into the unions/ bearing - careful how you handle it
You may not actually have to seperate the DPF from the turbo/ exhaust manifold
Old bolts can (especially on exhausts etc) be rusty spraying them with wd-40 / oil and letting it soak in can help, a bit of heat (a quick once over with a blowtorch) can work wonders
If you het "stuck" on something, leave it for 10, mins have a cup of tea, try again (seems like you know this one already!)
A Haynes manual can be very useful
When you are under the car, thilthy and covered on oil, sweat and you have skinned your knuckles and you are freezing cold, remember you have saved £45 on the checkup, an estimated £1000 for a new turbo fitted , so by douing it yorself you should be £800+ up - plus the respect of the chaps on the forum = priceless !
Much of it is common sense - not that that is common, in reality