Can I connect to Mac Mini Remotely from Mac book?
Yes. You can use OS X's built-in screen sharing. It's a VNC-based application that ships with OS X. You'll need to enable it on your systems in order to use it. Open System Preferences -> Sharing. And make sure 'Screen Sharing' is checked. I recommend the excellent ScreenSharingMenulet -- sits in your menu bar and lists any Bonjour-enabled screen sharing hosts in a drop down when you click on it for automatic discovery and easy connection to shared screens in your network.
Do I need to buy any other hardware for the remote connection or I can do thru Wi-FI available in both Mac MINI and Mac book?
No additional hardware or software is required. You don't even need ScreenSharingMenulet -- you can find and connect to shared screens via Finder if you like.
You do say something confusing your question though:
My aim to have a logical system with 12 GB (8GB with Mac MINI + 4 GB in laptop)for running Virtual Machines on both Mac MINI and Mac Book and be able talk to each other.
You cannot tie the machines together using screen sharing. They won't present themselves as one logical, virtual device to any virtualization software with shared memory or CPUs or any such thing. They will act as completely separate machines, but they can be accessed, graphically, from one another.
If you're trying to tie the machines together to act as a single, unified "super computer" you need to look at much more complicated technologies than anything OS X ships with. Beowulf for clustering and something better than ethernet for inter-machine communication will be necessary like a fiber channel connection (and that will require more hardware).
What about the performance compared to direct and remote connections as it is vital for Virtual Machine communication.
It is difficult to give an answer to this question as it all depends on what you're trying to do when it comes to communication between the machines. On the remote access side of things: over my local wireless network the performance is decent if you use adaptive mode on the screen sharing application but it can get glitchy if you disable adaptive quality scaling. If my macs are all on wires on Gbit ethernet then non-adaptive scaling is quite good. Processes running within VMs on my Macs have good sustained throughput to the Mac's built-in ethernet and wireless network interfaces. Inter-process communication between VMs running on separate Macs is going to be completely dependent on your network and your processes -- impossible to give an answer that'll cover all cases I'm afraid. If you get more specific with what you're trying to do I could possibly answer this more succinctly.
Our development team all use Macs. I have personally tried to use VNC both with Apples built in and premium Apple Remote Desktop ($79.99), as well as Jolly's Fast VNC. I had a Mac Pro tower at work and really needed the remote capability, and was able to work reasonably well with Apple Remote Desktop, but when my tower came off lease I went with a Laptop, because the lag and poor display quality were just too annoying. I found that I needed to degrade the display quality in order to keep the performance reasonable, which meant a blurry display. Overall I found it frustrating and avoid remote access, but it does work, although I would strongly recommend buying Apple Remote Desktop to get the full screen capability. Jolly's was fast but at the time had some bugs that resulted in a corrupt screen sometimes. That was over a year ago, the new version may be better.
There are other developers I work with who think that the VNC solution works just fine for them, so I think it depends a lot on how fussy you are about responsiveness (I am fussy).
If your previous experience with remote access involves Microsoft's Remote Display Protocol (RDP) then you will be very disappointed with VNC. The RDP technology is superior in both display quality and performance. One of the few things I really miss from the Microsoft world.
In short, I'd recommend moving to an Apple laptop and then running your Windows virtually. I started with a mini originally, and just ended up moving to a laptop eventually.
Best Answer
Port forwarding examples:
When you set port-forwarding on your router, you pick a port number (or range of ports) and a single local IP address, ie. port 5900 and Ip address 192.168.0.2. So any internet traffic coming in on port 5900 gets sent directly to the computer on the IP address 192.168.0.2.
Answered above, you've specified one of the IP addresses in the port forwarding. It will be the IP address you specified in the DHCP address reservations.
It's only as secure as your password. I'm sure that the password is encrypted before transmission back to your Macs.
You need to set up port forwarding in your Router.
Depending on your Router's make/model, the setup may vary, but the basics are the same regardless.
I would choose a port way north of 1 or 2.
Both computers will be listening on port 5900, so you'd set something up like:
85.85.85.85:15000 --> 192.168.0.99:5900
and
85.85.85.85:16000 --> 192.168.0.100:5900