Im using the dfrobot arduino romeos as these have built in power points for servos and motors so saves some messing.
The APC220's are what Im using, dead easy you just treat it as a standard serial port so you can basically do what you want. The way I have done mine at the moment is simply send 4 bytes from the pc, the 1st being a "command", the others being info for the command, for eg "M",50,2,0
The arduino code picks up the M,(move) then in this case 50 is the position to move to, 2 is the speed, the zero isnt used with my M command but I found it easier just to send a zero rather than working out how many more bytes to expect, the R command (raise) would be R000. Once the arduino has the 4 bytes, it sends back "OK", until OK is recieved by the pc it wont send any more - otherwise it can easily get confused. ITs a lot of years since I messed with any sort of serial programming and Im sure you can implement the RTS line but I have just done it my own way since it doesnt have any standards to comply to.
LCD's are odd creatures, well not so much LCD displays them selves but the controllers. There are several types, a standard LCD using the common hitachi 44780 controller is dead easy to use either with the built in arduino librarys or your own - BUT that one, like a lot tie up a load of I/O pins which is naff so for my other project (camera controller) I used an I2C graphic display so keeps plenty of I/O ports. The problem I had (lack of research on my part) was there was bugger all code readily available for the display (that I could get to work anyway) I got so had to pretty much do my own librarys with bits and bobs for the circle/rectangle etc modified from other peoples code - I'm not very proficient at all in C.
Heres an example of the GLCD I used, can of course display text, this one is a 128 x 64 pixel with a KS0108 controller onboard (I think its a 108, from memory, can check if you need me to) and was about £30. It can display 21 x 8 lines of charachters too - lot more versatile than the standard 2 or 4 line by 16 or 20 displays, and once you have the libraries setup you just LCD.print 'HELLO', or LCD.draw_circle (int x, int y, int radius, int color) etc etc

BEWARE, the dfrobot userguides have errors in the sample code !

Seems like we are almost exactly the same track here, shame we dont live closer.
Let me know if I can help in any way, I'm not too good at C as I said so my code is far from perfect, but I have some experience with micro controllers and some vb programming in general (did quite a bit with PICS years ago) but dont have a programmer any more which is why I went for the arduino - 4 arduinos is less than the cost of a decent pic programmer, plus theres no circuit to build.


Calv

GLCD Another

EDIT

Maybe you know this already, but there are 2 main variations on the chip used in the common arduinos, the 168 and the 328. The 328 has more memory and also quicker when uploading your program (sketch).