Which robot kit to buy?

I already have Vex Robotics and Lego Mindstorms kits (old kits with old electronics). I'm thinking of buying Bioloid Comprehensive Robot Kit which sells for $800. The kit could let me build any kind of robots but I have some arthritis and cerbral palsy. I'm worried that I may have problems assembling robots.

It's going to be a lot easier to build any pre-designed kit than trying to build your
own robot from scratch.

What about Lynxmotion Biped Scout kit which costs almost $180 or RoboBrothers RoboPhilo Humanoid Robot Kit which costs almost $400? Any tips?

I've never bought any of those kits, just built several walkers, quadrupeds and
hexapods, from scratch. As I mentioned, it would be much easier with "any" kit
than from scratch. I like the Bioloid systems, as they allow you to try out different
designs, but never wanted to spend so much money. Bipeds, in general, are much
harder to build from scratch, as there are many torque and stability problems to
solve, so I would probably go with a kit for a biped.

I ordered Lynxmotion servo brackets and other parts to build a humanoid robot like the one in the image:

I ordered Lynxmotion servo brackets and other parts to build a humanoid robot like the one in the image:

http://www.lynxmotion.com/images/jpg/ironmanl.jpg

Wow, the robot is really cool! How much of it? Are you buy some servo brackets and assembling it by yourself?

http://www.lynxmotion.com/images/jpg/ironmanl.jpg

You didn't mention if you bought the servos too. Bipeds like that have special torque
requirements on the hip and ankle servos, so you'll need to pay attention to the torque
values of the servos lynxmotion uses.

I already have six 240 oz-in servos, six 240 oz-in servos on the way to my house, two Parallax standard 43.1 oz-in servos, and four EZ-Robot S08NF standard servos. Any tips on building the biped?

I have no advice on this. Since you didn't buy a kit, you're largely on your own now.
You might be able to download instructions on building similar robots from the
lynxmotion site. To build a biped like the one you showed really takes a lot of work
and the program code will be very complicated - timing all those joints.