I feel like I've been gently and gradually sleep training my DD since she was 3 months old... like an extreme version of gradual retreat! From co-sleeping to next2me to cot in own room, she now sleeps all night in her own space unless she's ill (which she has been on and off all autumn). On this journey we have had all sorts off issues with super frequent waking to her being awake for 2h+ in the middle of the night.
Here are some tips, mostly to do with following natural inclinations and making small changes:
Put her down and get her up at the same time each day. My DD wasn't able to sleep more than 10.5 hours overnight, so our sleep window was 8 til 7 to allow time for one night feed, or 8 til 6.30 when she was night weaned. This stops the nightmare 2 hours wakes in the night as their circadian rhythm sets to that window.
Start very gradual night weaning. Baby doesn't need to eat every 90 mins at night, aim to shift those calories into the day. Start by dropping the feed at first wakeup. Once that wakeup stops, aim to space the next night feeds by at least 2 hours (they can easily do this in the day, so can do it at night too)
Look at some online resources for advice on night feeds by age, and use that as a template as solids become more established.
You want to encourage baby to get their calories in the day and sleep at night insofar as they are physically able for their age.
Try to avoid feeding to sleep at the start of the night, feed then do a story or a song, then put down and try to settle in cot when baby is suuuuuper tired. You can try pick up put down.
Don't sweat the early morning at this age. Feed to sleep, lightly cosleep if absolutely necessary so you can rest at 4 am without sleeping too deeply if you fear rolling onto baby. Sleep takes a while to come together, and that last stretch early in the morning is the last to consolidate. I would stop this by a year though, as baby becomes more aware and may start to form a habit you don't want.
Read everything you can, use what works and chuck what doesn't.
Ignore all the guilt trip bullshit like: hold them close, enjoy the cuddles, they are only so schmol blah blah blah mum guilt. Not everyone's life and circs are the same. You're reaching out for help, you need sleep, can't cosleep, and baby is physically capable of not waking 6 times a night.
Remember that babies are remarkable, adaptable, can learn new ways of being, and are on the whole capable of fitting in to family life within certain limitations (ie, still needing night feeding at 6 months)