I'd hang fire on the router... Granted it's a useful tool but I'm not sure it'd be near the top of my list.
I'd start by designing the cabinets you wish to make for the walk in wardrobe and then work out which tools will be most useful to that project.
With regard to the walk in wardrobe... I think I'd make a plinth to stand the units on to make sure everything is level. Then set about constructing individual units. You can then fix the units to each other along the plinth.
This will mean that the sides of your unit will face each other, therefore you could make your first project very simple by simply using screws and glue to join the main components.
BTW - classic error (especially if your first project is a wardrobe) is making something that is either too big to get out of the workshop or too big to get in to the house/room (wherever its going).
Chems guide rail looks very good but you can get away with screwing a length of contiboard (go for something about 6" wide to ensure it does not bend sideways) to a wider piece of board and then running your saw along the edge of the contiboard (cutting the second board at the same time). You then have a cutting guide where you can line the lower board up to your cutting marks and away you go.
Also... when cutting board... get yourself some sacrifical pieces of wood to go under the board you're cutting. The saw blade just cuts in to the top bits of the wood underneath leaving the board you are cutting fully supported at all times (i.e. you're not trying to catch the offcut).
