Welcome to the daunting digital Rabbit hole! My suggestion is to step back and look at the forest not the trees to see where you are and where you think you want to go before diving in.
You have a nice entry level DAC. Many will suggest a similarly priced streamer to match and that would be perfect if you content to just have a foot in the digital door. However, as the guys at Linn say "Garbage in equals garbage out", so a better streamer will make your DAC better. I think your plan to spend more is good. You can upgrade the DAC when it suits you.
Streaming software's sound different. The Innuos Sense App sounds better to me than Roon and is free and integrates perfectly with Qobuz and I've used it with Tidal with no issues, so I feel Innuos is a great choice. I bought a used Innuos 5 years ago and love it. Support is excellent, updates are free.
As far as connection, for simplicity start with USB. In my system USB is not best but that doesn't mean it is awful. I spent time on the I2S bandwagon and it was better with some DAC's and not with others. I use S/PDIF (with 3 DDC's) now and am planning to purchasing an AES cable hopefully soon as I think it will be better. You can always add a DDC to swap connections if you get the itch down the road.
Keep it simple and have fun!