I agree with you. You say your students are beginner level, so it’s a good idea to do some work on basic language patterns before you start work on IELTS preparation. I suggest you start by presenting or revising the major tenses and by working on vocabulary. Try to make this initial work as communicative as possible: give the students plenty of opportunity to use the language orally. Use written texts and recordings to present the language; by doing this students will get practice in speaking, listening and reading whilst improving their knowledge of basic grammar.
The amount of time you spend on this will depend on your students’ level and when they are planning to take the IELTS test. When you have almost completed the basic language work, you can start on test preparation. I haven’t prepared students for this particular test (I’m more familiar with the Cambridge UCLES exams), but the principles are the same: give students plenty of practice in what they will be expected to do in the test and teach them strategies for dealing with the test, including time management in the test. Here is a list of books that help candidates prepare for the IELTS exam:
During the initial stages, you can do mixed skills lessons, but as you get closer to the exam it is preferable to focus on one module at a time. The students will be tested on the skills separately, therefore it is essential to teach and practise them separately.
From your questions, it sounds as if you are on the right track. It seems as if you have all the answers yourself; well done!