From an i5 4460 to an i7 7700, there will definitely be an improvement for performance. You can check this.

A possible wallet-friendly upgrade is to trade up your i5 4460 to an i7-4790 or an i7 4790K if your existing mobo supports OC.

Yes quite significant and worth the extra RM 100+ for 7700K, the stock speed difference is 0.6GHz when turbo boost is off (4.2G vs 3.6G) and the most important thing is quad core turbo boost on 7700K can stay at 4.4G while 7700 can only manage to do 4.0G, but bear in mind you will need to spend extra for an after market CPU cooler too because 7700K doesn't come with stock cooler.
You need to look for previous generation chipset (namely H110/B150/H170/Z170) with DDR3 RAM slot to use DDR3 RAM with i7 7700.

As Terence mentioned, you will need to get older mobo that supports DDR3 for this purpose. Unless your plan revolves around reusing existing DDR3 that you may have, it is actually better to get on the current DDR4 platforms. You could always sell your DDR3 in GS