Re: Your draft board
Kanter-His skill level is very high at this age, lack of development this past year is concerning though. If his back checks out, I would have no problems with the pick. IIRC, he measured out well as a centre in the Combine too. Could be a solid, offensively productive centre in the Kaman/Gasol/Horford mold
Val- His weaknesses IMO are all ones that can be developed at the NBA level (weight, more advanced post game, etc). He has the size and plays exactly how you want your centre to. He's also had production in the Euroleague and has rebounded well in a man's league. Chandler/Biedrins/Noah are some comparables in the best case.
Knight: He reminds of a Jrue Holliday type of player (not exactly top 5 material in a good draft). However, he has shown he can play the P&R which I think usually translates to the NBA (not to the same extent as rebounding though). It may present problems however if the Raptors choose to go with a Knight/DeRozan backcourt in terms of ball handling, I don't see any great playmaking coming from that backcourt.
Biyombo: Haven't payed much attention to the whole age issue with him but he could also be that defensive oriented centre that Val may project to be. I think it's a tall order to make Ibaka comparisons (Serge has developed at a ridiculous rate esp. for an foreign prospect) but by all accounts he's a quick learner too).
Walker: I see him as a solid change of pace guard in the Aaron Brooks mold. Draftexpress has his best case as Lawson which I would be ecstatic with but I don't see the same quickness.
I really don't like Vesely. Poor shooter (both outside and at the FT line) and his handle looks really sloppy. He may be an exciting player on the next level, I just don't think he'll be a productive one.