Road Bike Brake Calipers

No. There are a couple of mounting options, 'direct mount' and regular. Some calipers are available as a 'long drop' version, these fit frames with more clearance between the brake mount and wheel. Different manufacturers have different 'quick release' options for removing and fitting wheels. As with other components it is recommended that you use the same model of caliper as the rest of the bike's groupset (groupset finishes often feature different finishes, so mixing calipers between groups can look a little odd).

While hydraulic disc brakes offer more braking power, consistancy and modulation, there are still lots of road riders who prefer rim brakes; Rim brake bikes tend to be lighter and wheel changes can be quicker (than disc brake wheel changes) too. There are also lots of excellent rim brake wheels being made, and still lots of rim brake spare / race wheels sat in sheds and garages.  

There are a few things which typically effect performance of brake cables through regular use.Brake cables are susceptible to water, dust and dirt getting between iner and outer cables. Lubrication between inner and outer cables can also become less effective and dry out. Bikes with trickier cable routing (through handlebars, frames etc), can suffer noticably worse braking peformance when cables are due for replacement. Damaged or split outer cable, ferrules and guides can also negatively effect performance. 

Disc brakes offer more powerful braking and smooth modulation. Disc brake bikes feature through axle mounting for the wheels, this provides a more solid connection between the wheels and frameset. However! Many riders don't need powerful braking and don't want the extra weight of hydraulic bisc brakes, in addition riders with rim brake race wheels might want to keep using them.

No. Gear cable 'inners' are thinner, usually 1.1 - 1.3mm as opposed to 1.5 - 1.6mm for brake cables. Cable ends are also a different on gear cables, compared to brake cables. Gear outer cable has horizontal strands to resist compression forces, where as brake outer cable is wound from a single wire (under the protective top coating).

There are a couple of options with brake blocks (or pads). Most blocks slide into the block shoe / holder which attaches to the brake caliper, some do not - so you would need blocks with shoe / holders. Most blocks are designed for use with aluminium rims, if you ride carbon wheels, you will need carbon specific blocks which perform better on carbon surface.

We always recommend following manufacturers instructions for fitting any component. The Youtube channels of Park Tools and GCN Tech have very indepth and comprehensive advice for completing all sorts of jobs on bikes, these are also worth watching particularly if you are inexperienced or unsure.