I am afraid you need to be more specific on what you planning to do. But in general, If you planning to write 3D unstructured code, for laminar and turbulent flows then no need many open source codes already exist for that such as OPENFOAM, Code_Saturne, fluidity you just need to pick up one of those and try to use it to solve your problem. If the idea is to start from simple 1D problems then I suggest starting from the simple 1D Fortran codes provided by Fergizer and Peric. The link to those codes can be found in their book "Computational Methods for Fluid Dynamics".

I understand that you want to write your own code, not to use an open source, good idea to get much more familiar with CFD. I suggest either the Ferziger and Peric book as Yacine above suggests or the book by Patankar (Numerical heat transfer and fluid flow) using one of Simple variants (Simple, Simpler, Simple consistent - check also a Raithby article) and sit down and write it. I went the same way about 25 years ago and this was very nice and exciting experience. And for the beginning you do not need to use unstructred grid, use a simple structured cartesian grid. For curved boundaries you can use the so called staircase boundaries. As for the conjugate heat transfer, you simply define solid domain with extremely high viscosity (using xlarge source term) and in this way you block the domain for fluid flow. And later you can proceed with unstructured grid - but this is much more complicated.