ummm, where can you find a 60mm or 70mm case fan?
212 Evo has been replaced by 212X, but you'll still find 212 Evo around certain stores in Low Yat Plaza.

You can, why not? but do take note that having just holes will block some airflow to the fan, unless there is little gap between your drilled holes.

I'd suggest that you just cut a hole and get a fan grill, you can get the basic ones like these for about RM8 in LYP



or you could make one like this out of arcylic... or aluminium if you have milling machine

I would recommend you to do so, helps minimize the amount of dust but it's totally up to you, some people don't because they wanted the fan to look nice lolz

a filter is needed if you wish to reduce dust intake, since your case will be placed on the floor.

It'll be better if you can find someone to laser cut for you, cleaner cutting 

not sure about the pricing, but here's your place to go:
http://www.lasercut.com.my/index.php

a small cut won't cost you Rm100 i think?
can try to ask them the pricing maybe.

well, you can ask the price 1st, if it's okay then you can consider to go for it.
unless you're an expert in cutting metal stuffs, I tried to cut my old ayam case once, never again i will do it again. 

Well, i got uneven cut as result. The thing you should be prepared which i personally think is some skills