Need help deciding components

Ok so i work for a company as an apprentice i will be building them high end computers which they need for computer aided engineering but theirs one problem i dont really know what the best motherboards Cpu's etc are or whether they will fit together the cost of these could go up to £7000 which is alot of money so i dont want to waste it on junk. so what im asking for is help to find components which will fit together, the company has told me they mainly want a Fast CPU, Fast imput/output and a high end graphics card, i also what to know whether i can put 2 graphics cards together and a few hard drives together etc what i would be able to do to max out this computer

My company has decided to go with Xeon x5690 processor so i need components to fit with that

They use Ansys to do engineering simulations