Don't forget to plan for future posting and ways to make users interactive, such as commenting and tagging their friends. So since this account is fairly new, post 2-3 times a day. Give a reason to have users follow you back.
If your goal is trying to reach 80K-100K in less than half a year, then you should in no doubt invest a bit of money. If the reason is that you don't have a credit card to use or some bs like that. Go get a $25 prepaid card and start with that.
If your content is legitimate and creative than your follow back ratio for every 10 followers will be 2-3 (20%, that's a realistic amount). So the last time I was active on insta for a niche of mine, the limit of following and unfollowing was 20 per hour, but it might be 160 per hour tho. But that's for you to test out. The limit on liking is 350 per hour. The limit for hashtags on each post is 30. So a guide for you to follow is this:
1. On your niche topic, research top 30 tags on your niche and write them on your device's notes
2. Scrape up a total of 30 pictures to post (that's 10 days worth of posts)
3. Find the best times to post for your crowd. (So for east coast US that's 8:15 am, 12:30 pm, and 5:45 pm: morning before breakfast, after lunch time, and before dinner. Those times are recorded the best for my marketing. It will be different if your targeted crowd is somewhere overseas, but relatively the same hours)
4. Depending what your test results, follow as much as you can per hour of the day. Follow X amount of people who follow Instagram accounts in your niche.
5. Go through all the recent posts of the hashtags you choose to post, and like all the recent ones.
6. Repeat all steps for the following week.
Following this this guide will get you pretty darn close. And as for the $25 I mentioned earlier, you will be using that for either two options.
1. If the method is gaining no followers to your account, go ahead and head to the marketplace and buy followers, with $25 you'll get somewhere around 3k followers or less.
2. If the method is overwhelming you, sign up for instagress and spend some time tweaking the bot. $25 will give you 5 months of use, if I'm not mistaken.
So it's time for you to get your hands dirty and busy, good luck OP and keep us posted.