Before considering any other instruments, you need to work out how to get good recordings of the drum kit, since it's relatively large. Your big problem is going to be the acoustics in the rooms if they are untreated. You are not easily going to get the "high degree of isolation" that you mention.
Since you have indicated this is to be more than just a demo recording, and also that you can nail the rhythm parts of these tracks in only a couple of takes, for this first CD I would seriously consider renting professional studio time for recording the drum kit (which needs many microphones) and also the bass (via DI), and maybe rhythm guitar too. You can take those tracks away, and using them as a bed, make do with adding lead guitar and vocals in a home studio with a lot less expense on gear and acoustic treatment than you would have needed for the whole band.
It's likely that this is not what you wanted to hear, but a professional-quality recording of a full rock band does not just happen - it takes more than a reasonable amount of cash thrown in the direction of purchase of equipment. That said, the difficult bit is the rhythm section, and if you get a helping hand for that, you can add the overdubs and then enjoy the whole mix process without having to battle with problems created by poor acoustics and track bleed.