Derek -- I just cleaned my bike inside for the first time and I used a 5 gal. bucket from Home Depot and warm soapy water. With the bike in the repair stand I put the bucket under the section I was washing and using a rag washed the area and then moved on. I had a tile floor area to work on, but if you don't I'd buy a plastic tarp or a heavy plastic sheet to work over.

For simple road grime, soap and water worked well. For oil and grease and tough stuff I used Simple Green which did a good job. I'm not sure my bike is as clean as it is in the summer when I can use the hose and a lot more water, but it looks reasonable.

Coincidentally I changed my cassette this past weekend and found it to be pretty easy. You'll need a chain whip and the correct freewheel tool, plus a large adjustable wrench. You'll want to make sure you have some grease to lightly lube the freehub before you put on the new cassette. I wiped a little bit of crud and the old lube off the freehub with a rag and mineral spirits before relubing and installing the cassette.

Once everything is clean just relube everything, check all the fasteners to make sure everything is tight and check any other parts for excess wear. Good luck.