If you post your layouts and schematics (as images) we can critique them. This sounds like quite a project, so I definitely recommend trying to get people to sense check your design.
Fully-assembled is an exceptionally expensive way to buy prototype PCBs. Something that takes an hour or two for an amateur to assemble will take a professional longer because they really have to check it and test it before it goes out the door.Even in China, those professionals don't work for $5 per hour.If this is your first PCB then you will certainly make a simple mistake. Do you want to spend hours on the phone with the assembler or do you want the $4 PCB in your hand so you can look at it and see you forgot one power wire?I got into PCB design because I had a project with one particular component that was only available in surface-mount. (The ADXL345 accelerometer.) With a "laser" infrared thermometer and a frypan on the stove I was able to build that project on a PCB with very low cost in dollars or hours. The only delay was waiting 2 weeks for the version 2 PCB with the power trace I forgot in version 1.