I've never had problems ordering custom hardware from my dedicated server providers. At worst, all I've had to do is pay a one-time fee for a particular component. SSDs have never been a problem. Neither has any Intel CPU.

It of course depends on your provider.

Rent vs buy depends a lot on the circumstances. Maybe if your requirements don't change and you don't upgrade your server hardware it's cheaper in the long run to buy. However, when I've kept a server for more than a year, I've always been able to negotiate a discount.

You didn't post your config, so I can't tell how exotic your requirements are.