First off I will start by saying that I haven't used Ruby on rails so wouldn't be able to advise here. What I have read though is that in the past RoR may be considered over another platform such as javaee as it was considered easier to work(a one stop shop) and more lightweight. I'm not too sure whether this is the case now as java is in the process of stripping down its specs.
I would consider using Java/javaEE(6) platform in particular JPA2 (data layer). This will allow you to use an ORM to map your database tables(relational model) to objects, EJB3.1/managedbeans (business layer which also helps with code re-use and concurrent data-access) and JSF2 (a framework for creating UIs) or JSP as the presentation layer. There are many tutorials online and the majority of the documentation is published by Oracle.
I guess security-wise it is often the best idea to implement application server managed security as then you are relying on (hopefully) the fact that a security professional was consulted in the implementation of the app server. In a recent project I achieved this using Glassfish managed security which made it easy to hook up existing user/roles already stored in the database that would then control access to the application using URL patterns or whatever - a service like this is usually very customizable and may even have a GUI settings page in your chosen app server to aid in the configuration which will make life easier. Again this really depends on the application server you will use. It may be easier to integrate your oracle database with an oracle application server (WebLogic). There is likely to be similar functionality as to what I have explained about Glassfish.
You could also implement security at the EJB level which means that you can specify explicitly which roles can call which business methods. This may be over-kill but always something useful to bear in mind.
With regards to connecting to your database - would it not be easier to work with it using an IDE? Also, perhaps a useful feature for you as you already have the database made is to create your model entities from the database automatically using a tool. Netbeans supplies such functionality and it means that as long as you can connect remotely using the IDE you could create your data layer and a basic business layer with basic CRUD operations for each entity in <5 minutes (give or take). An understanding of the platform/relevant frameworks may take longer though.
Again check out some tutorials/docs on this. I'm pretty sure Netbeans can make your life easier if you are working with WebLogic as well.
Again sorry I can't shed any light on RoR. This is my personal suggestion and you may want to listen to others thoughts on the subject as well.
