The basic advantage of a roller cam is that it gives you more area under the lift curve. Let's say, for example, that you are comparing a solid flat tappet cam and a solid roller cam that have exactly the same advertised lift and duration numbers. On the roller cam, the ramps can be steeper on the flanks of the cam lobe, and so the valve opens more quickly and can stay at the higher lift levels for longer periods of time. This gives better cylinder filling on the intake side, and better exhaust scavenging on the exhaust side. The roller cam has this advantage because roller lifters can follow a more aggressive cam profile. So generally a switch from a solid cam to a roller cam with equivalent specifications will make a significant performance improvement.
In terms of installing a roller cam, you just have to make sure you have the right components. You need the roller cam, the roller lifters, and better springs than you would use for an equivalent flat tappet cam, because the higher opening and closing rates will need more spring pressure to keep the valvetrain under control. You also might need better pushrods, depending on the springs, and titanium spring retainers are also a good idea. Finally, most roller cams are machined out of steel rather than cast iron, and will quickly destroy a factory cast iron distributor gear. So replacing the distributor gear with a steel or brass gear is also going to be required. Other than that, there isn't really anything special you need to do. Just make sure you get good components that are matched up well with each other.
To answer your questions more specifically, probably figure an additional $600 on the cam and lifters for a roller over a solid, $80 for a steel distributor gear, and maybe another $300-$600 on springs and retainers, depending on the cam requirements. Whether that is worth the additional torque and HP is up to you, but on an engine like yours it wouldn't surprise me to see an increase of 30 HP and 30 lb-ft of torque with a change to an equivalent roller cam. Regarding engine speed, the hydraulic roller stuff can be made to go to 6000 RPM if you have all the right equipment, but often it will only get to 5500 or so before valve float sets in; this was the problem with the Crane hydraulic roller setups you mentioned. Solid rollers, of course, will go higher.