IMHO: For a beginner, the fastest CPU you can afford with at least 8GB would probably be the best choice. Even better if the RAM can be increased later. I suspect that most beginners will probably not outgrow 8GB in less than a year, more likely two if at all.
i5’s can be faster than i7’s (&Zeon’s)
The CPU with the highest MHz will be the best for drawing in Rhino.
Rendering can be faster with extra cores/threads; if you use a CPU based renderer and actually plan to do rendering.
Best bet is max out your CPU and go for 8gb ram (as per other suggestions). Ram is easy to upgrade; and generally gets cheaper too
You should also consider, that RAM right now is absolutely cheap to get.
today you get a good DDR4 16GB 2400 kit for less than 60€ (germany). so why not just get more, regardless if you need it or not. its just so cheap
thats why I went for 32GB, paired with an i5-6500