With the basic dimensions it was on to some of the intial details.
Time to start working out how things will go together. For a Newbie's first solid wood project the idea is to go with simple, easy to do, joinery based on the tools and machines available. Fortunately I have a pretty well equipt shop so there were plenty of options.
We could go with just glue - but end grain to side grain glue joints aren't very strong. The KREG pocket hole jig would make pocket hole joinery quick and easy - BUT - since there will be doors - visible pocket holes on the inside of the doors would be ugly. We could biscuit join some of the joints - but there's the grooves for the panels. We could go with tongue and groove, or groove and splines - or we could do loose tenon M&Ts - with my DOMINO. I described each alternative and did some quick sketches to illustrate how each was done and worked. I also did a DOMINO sample on some scrap. The DOMINO was clearly quicker and easier - so we went with it.
Now we had enough specifics to at least work out how much wood would be needed - poplar since it's relatively inexpensive, easy to work with and can be stained to look like just about any wood.
If the rails and stiles are to be 2 1/2" wide - and we've got FOUR 8' stiles for the frame and side panel and EIGHT more 8' stiles for the door frames we need - so - we need boards we can cut TWELVE 3/4" x 2 1/2" x 8' stiles from. AND we need wood for the rails as well. The 2 1/2" width isn't super critical so if it's half a saw kerf narrower - that's OK.
And here's where the fun starts. The BORG'S sells S4S (surfaced, four sides) boards by the "Lineal Foot", with nominal widths which are actually 1/2" to 3/4" narrower. That's a problem when a newbie goes to get wood. Four 2 1/2" rails should come out of a "1x10" - forgetting the saw blade's kerf width. But when the actual width of the board is measured - it's 9 1/4" NOT 10".
If we'd had a more accurate, detailed plan for the linen cabinet, I could have put together a Cut List, determine how many parts of each size - and thus how many 1x6s, 1x8s and 1x10s (1x10s if real wood raised panels were going to be used) would be needed. Alas, the Get Most Of This Thing Completed Over The Three Day Weekend didn't give me that luxury.
So she got the poplar boards and she ripped the stiles and rails to 2 1/2" width.