Hey Joe — good question and something I found a bit of a struggle at the start.
A few of things to consider:
Firstly, took me ages to settle on a theme. Endless scrolling online, crazy amount of presets. Then realised I just needed to pick one. Doesn’t matter if it’s the wrong one, the main aim is to start building up an aesthetic to create a sense of consistency. You can change later if it doesn’t suit you (but yes, you’ll have to build back up again).
Alternatively, you’ve got a lot of apps out there that can help you out. Look at ‘Mosaico’ — you can plan your Instagram feed to see what it’ll look like. So if you really don’t want to commit to a filter, try it out on that.
Thirdly, if your strategy is to have multiple themes, that is in itself a ‘theme’. Like I mentioned in the post, you can do a row of three using one filter, a row of three with another, and so on.
Instagram really is your oyster — play around. Hope that helps!