If an R56 is gonna be left in the garage for more than a month or more without being used
1. what issues might it encounter since the engine will be "sleeping" for a long time?
2. what is the best way to prevent from these issues to happen?
3. will disconnecting the battery be a good way to solve the issues or might it effect the electronics of the car?

 

You could well run the battery down to zilch, which at least isn't good for it, at worst can kill it. Solution is relatively cheap - pick up a Battery Tender, they work VERY well...

http://batterytender.com/automotive/...-at-1-25a.html

 

Up to a couple months storage there is not alot you have to do.
DO NOT disconnect battery but invest in a trickle charge (battery tender). The one I use on my Harley was like $45.
I'd put some Stabil in the gas and fill it up.
Lift wipers from glass so the rubber won't deform.
Make sure tire pressure is up so you don't get flat spots.
Other than that nothing.

 

why not disconnect the battery?

 

If disconnected too long it can screw your electronics up.
It's not like the cars were way back when.
If battery is disconnected too long you can lose stored codes.
This is what I mean by screwing your electronics up.
Not guaranted it'd do it but possible.
How long are you storing it and will it be in a garage?

 

This is not true; any fault codes or hard-coding will not be lost due to power removal.
That information is stored in the non-volatile memory of the ECU.

What will be lost when power is removed is things like radio pre-sets, radio security (like anti-theft), no active alarm system, etc, etc.
As KevinC suggested, grab a battery tender.

- Erik

 

^^Maybe but I'd still just put a battery tender on it. Sounds like he's only storing it for a month or two.

 

im storing if for a month to be exact!

 

^^Yea, if you can afford it I'd invest in the battery tender. You can probably find one on the internet for around $35 but than ship will kill ya.
I checked online and found them cheaper than the one I got at the Harley shop but with the ship it ended up being the same, around $45.
You can leave it plugged in and it will not overcharge your battery.

 

Only a month? Hell I would fill the tank, do a full detail, and then throw a car cover on it and call it good enough. I have stored 2 cars for almost a year 3 different times and there are not a lot of problems that are going to develop in a month of storage. I am also assuming that your MINI is less then 3 years old.