Due to circumstances partly beyond my control (and off-topic) I've porked by bike's drive-train. It needs a new chain, new cassette, and new chain-rings. Or maybe it's not (completely) my fault, as it's been through at least four chains and two cassettes; maybe it's just that time.

Bike is a 2010 Giant Transend 1 - https://www.giant-bicycles.com/au/transend-1-2010

I've previously replaced the SRAM PG950 11-34 cassette with (IIRC) a Shimano HG80 11-34. Right now, it looks like I can get a slightly better deal on an XT M770 11-34.

The crankset - 26x36x48T - The BB is an internal sealed-bearing, and it's like new. Can I even get a crankset to fit this? Or is everything external-bearings now? I have a spare crank-set off-site. IIRC it's a Deore M590.

So...

Can I find a new crankset that fits the internal-bearing BB? Or do I need to "upgrade" from the BB?

How much of this should I do myself? How much of this should I pay the shop to do?

I actually like the chain-guard on the old crankset, but I can't find any new cranksets with a chain-guard. What's up with that?

Any other thoughts, considerations, or advice here? Thanks...