You could check a used bookstore or libgen for textbooks to learn grammar and have basic examples, use the smartphone version of pleco for a dictionary and free notecards based on the different hsk vocab levels. Also please study grammar, don't use the duolingo model. To practice writing characters look up tianzige （田字格）and write each character a lot of times and say them out loud as well. It helps if you start with some radicals, I think there are 40 major ones (at least my textbook listed ~40 major ones). To type characters, I recommend using the pinyin layout, you don't have to type the tones but it will guess them and give you options. Other typing options and handwriting input and strokes. You can translate chinese to chinese on google translate to get pinyin for larger texts, and deepl will translate with better grammar and syntax if you need that. The hardest parts if you're doing this alone will be checking your work if you're doing exercises, since you won't have a teacher to ask questions and explain your mistakes, and it will also be hard to practice speaking and listening alone. For basic pronunciation I am not sure what is best for free online options. There are children's songs videos for bopomofo which covers all initials, and there may be ones for the finals. Google translate or pleco will have pronunciation for characters and words, but whichever I used pronounced each character individually and did not give you the tone sandhi, which is the change that happens when pronouncing certain tones in order (not as hard as it sounds). You should also read the wikipedia page on 儿化 (erhua) because even if it is in your textbook it probably won't give a good explanation. You can find podcasts for basic listening by searching 学中文 （xuezhongwen) or 学汉语 (xuehanyu) on any podcast platform, though you shouldn't immediately start with this, it is at a late-beginner early-intermediate stage that it may become useful. You will probably gain listening abilities faster than reading ones, but you could also look for graded readers. I haven't looked into them too much at my stage of learning but what I have seen is paywalled so I can't offer much advice there.