Ravi, well done on the RPL - step one out of the way. A few thoughts over which you might mull.
1. I'll leave this for Bob/Stuart as I don't have the two documents to which you refer in front of me for comparison.
2. You will need a mechanical computer for three reasons - the examiner won't let you use an electronic device, if your instructors are worth their salt, they will require you to demonstrate competence on the basic device throughout your training and, although not an everyday event, if the electronic device fails, you have a mandraulic backup. While many folk use one of the electronic devices, I can't see much value in them as you can do all this flying stuff using traditional methods in much the same time and retain the understanding which the electronic units tend to destroy.
There is a host of different navigation computers which have been used over the years, but two basically have swamped the marketplace. Both were developed in the between wars period and, during WWII, both were used, near exclusively, by the various militaries. This use then captured the post-war civil marketplace. The allies used the Dalton device, developed by Philip Dalton, a US military engineer/pilot, while the Axis used the Dreieckrechner, developed by a very bright German engineer/pilot, Siegfried Knemeyer.
The US device, originally introduced as the E-6B designation in the US military, subsequently was produced by numerous civil manufacturers once the patents expired and these, generally, were known as E6-B or E6B computers. The German device post-patent was further developed by Ray Lahr at AA. Rights to Lahr's device were purchased by Jeppesen and the unit became known as the Jeppesen CR computer. This device, now, is produced by a range of manufacturers. One sideline consideration is that one manufacturer chose to style its version of the CR as a "circular E6B" which was both a bit silly on historical principles and tends to confuse the issue somewhat.
As to which you choose to use, that is largely a matter of personal choice. Each is fairly straightforward to learn. Considerations include
(a) the Dalton, usually of aluminium construction, is robust and will take a lot of pilot punishment. The CR, being plastic is susceptible to heat damage - leave it on the coaming on a sunny day and plan on buying a replacement.
(b) most implementations of the Dalton use incompressible solutions for the TAS calculation. This is fine for light aircraft but requires a correction for higher flying, faster machines. The correction is simple and several units come with the correction incorporated. However, the typical Dalton, without the correction, is not suitable for ATPL exams as you won't be permitted to take in a correction table and it is a bit complex to memorise. The CR units have both the incompressible solution (as for the Dalton) and the compressible solution which makes them a bit more versatile. Generally, the CR units have a few more things incorporated, most of which you are not likely to use.
(c) the Dalton has a slide and is bigger, physically, than the CR. The smaller CR units fit nicely into one's shirt pocket.
(d) the Dalton probably is a bit easier to learn than the CR but there really isn't much in it. There are various differences on the calculation side but the main difference is with the wind solution calculation. The Dalton is a straightforward triangular vector solution while the CR uses a trigonometric solution - two ways of looking at the same thing. While it helps to understand what is going on, both can be used in a by-rote fashion, providing that the pilot doesn't forget the step 1 - step 2 etc sequences. Due to the trigonometric solution, the CR has sine (or cosine) tables built in which may be of value to those who are interested.
3. You will have to do the exam using a mechanical device. What you use in the aircraft is up to you. I wouldn't bother with an electronic calculator as the mechanical device is a doddle to use and the accuracy is more than fine for practical purposes.
4. Difficult to call. Treat them in a manner where the RPL covers the basic stuff while the PPL extends on that basic knowledge. Similarly, the CPL is just an extension beyond the PPL.
5. I would use both the RPL and PPL books so that you cover all the requirements of the syllabus.
