Server for the loaded project?

Everything you need to grow.
If the project yet, take server core to four...
Then if the project will grow and bring money can grow.
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And take a cool server under covered projects, IMHO not necessary :)

Cheaper one powerful server. First and foremost, you need to follow the powerful channels and a OP for the cache. The PERC is almost always possible to save.
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I'm under a download of the collected Core i5-750, 8 DD3-1333, 2 * 1 Tb. But the site has not received such loads.

I will say one thing: 150.000 hosts a day is not 150.000 online. with the conventional recoil handle conventional lamps of the UPU. but online is quite another.

The main thing is really not in the server... it is Very important to minimize the number of calls to the database, to separate the results of statics from the main kernel (in this case the kernel (LAN port, hard drive).
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Also, the performance-based — as quickly as possible to let the user (tobish not create SMO not to pull AJAX every second) —
as quickly as possible to issue the result on appeal, and otherwise drown the server with 192 cores and 512 GB of OP.

Start with a VPS with lots of RAM. A good server is worth good money, 100k a day you definitely don't immediately drive.
Then you can rent something, and when you get to your required metrics then buy. And then just the headstock is drained on resources that are a year need only. A year later, the grandmother will be possible to take something tastier :)

1) it is impossible to say according to this. You have not specified the peak load and it is unclear how fast the processing of a single request. Minimum 2: database server and application server :)
2) how to make it. Google collects a cheap iron, but iron very much.

150,000 queries, it is just 1.7 sec.
How many runs a single request and how many resources it eats? will not work so that not having to stop the first request starts the tenth and the workload will increase...