Visit some of the other "first rack" threads. The biggest issue in almost all of those racks is the SIZE of the rack. They are too small. Skiffs should be built by people who really know modular well. To build a GOOD skiff, you have to make trade-offs on your modules considering size and features. My analogy is that it's building a classic Swiss wrist-watch versus a grandfather clock. The wrist-watch is much smaller and the tolerances are a lot tighter. You're going to get into a lot more trouble building the wrist-watch coming into it with no experience.
The first thing that is problematic is the control of your synth. Plaits requires a pitch CV and a gate CV play, so does your BIA. Every Erica drum module requires a gate/trigger to play. Where are all of these triggers, gates, and CVs going to come from? The MIDI module you've dropped in is very basic and can't support that many modules itself.
Speaking of the number of modules, how do you intend to get every sound generating module to your audio outputs? You can use the Maths as a basic mixer. But that's a huge waste of a Maths module. You have two oscillator-type modules, drums, a noise module, put some time into picking out at least one basic mixing module. You might want something basic that can handle audio and CV... and then maybe something a little better that can handle stereo audio.
It's been stated "you can never have too many VCAs." You have too many VCAs... for the size of this build. Plaits and BIA have their own internal envelopes and VCAs as well. You don't have to use them, but most people do.
I have DATA and I have Maths. But they are nice-to-haves in a Eurorack case. For a skiff, they are just too big to justify in most cases. But again... why skiffs aren't a good idea for your first build.
Also, the 2HP stuff should be integrated sparingly. The tiny knobs are tough for big fingers to adjust accurately. Also, if you place them next to each other you will have a really hard time not bumping the settings for an adjacent module. You'll find in Eurorack, that tiny adjustments can be the difference between a sound that's garbage and one that takes your breath away. Ergonomics is a real thing. With 2HP modules you also have to keep careful track of your power consumption as well as the DEPTH of space available in the case. 2HP modules can run pretty deep in order to keep their 2HP width.
I hope this reply was helpful. If you bought this set-up as-is, you'd probably be disappointed.