1.C 1 and TEM4 are not in the same level at all. I'm not sure about your level of TEM-4 simulation, but this test for TEM-4 is given by domestic teachers, and the test focuses on grammar words and so on. There are not many real investigations about German language ability. And the kind of exams that foreigners take, such as A 1-C2 of European language proficiency, Telford exam, etc. Everyone pays great attention to the accumulation of language, especially the ability to talk to native German speakers, including whether you can understand and talk to him. I have passed TEM4 and Telford, and I can tell you responsibly that TEM4 is far from C 1!
2. I haven't taken distance courses, because I am in Beijing, so my friends around me will choose face-to-face courses instead of distance courses.
3. Again, these are two almost completely different evaluation systems. If you want to get good grades in CET-4, you should remember more grammar and words. Therefore, this remedial class is only of little help to CET-4.
In a word, to put it bluntly, it will be more difficult for you to take the C 1 course now. After all, in view of the limited German teaching resources in China, there is little or no teaching environment in pure German, so all majors in Grade 48 pay more attention to writing. Let's prepare for CET-4 with peace of mind and review with the teacher. Goethe Institute, a training course to improve German ability, is not too late to go to Band 4.