Answering your cycling questions

Replacement is straight forward but you need different cranks (Hollowtech II type) to go with this bottom bracket.
Difficult part is to prepare your frame before fitting hollowtech II bracket first time on the bike. Basically you have to face the frame to avoid future problems. The term refer to making sure the surface of the BB are "parallel" to each other respectively. There is a very expensive tool required to do this. I suggest you get this done in one of Evans workshops.

Yes, this should be fine

Should be fine. Have a look at the chart by Shimano showing compatibility: http://bike.shimano.com/publish/content/global_cycle/en/us/index/tech_support/tech_tips.download.-Par50lparsys-0025-downloadFile.html/01%29%20Drivetrain%20Compatability%20Chart.pdf

Hi,
Yes it would be fine with those cranks.

yes, however is for road riding and will not stand up to the abuse from a mountain bike ride

Yes these will be compatible with the tiagra 4500 system.

Yes this will work with a 105 chainset no problem. Yes you can mix and match shimano road part for BB and chainsets in this way without any compatibility issues, the difference is in the materials used.

Unfortunately not as FSA cranks have to go with FSA bottom bracket they are not interchangeable.

Yes this will fit fine the BSA means its a british thread which i assume is what you need.

You could but you will need to buy new cranks and this BB is for a hollow tech type crank set.