Thanks for the lengthy reply

If you want to make hard techno, by this I assume a bit in the styles of Charlotte de Witte or I Hate Models, you will needs loads of effects. I'd advice to keep your standard reverbs, delays and compressors in Ableton, otherwise it'll take up a lot of space and money. However eurorack effects can be more interesting as their parameters are often easier to modulate. The FX aid pro seems to be a reasonable choice as it offers a load of different effects. Maybe you can also look into the Endorphin.es ghost, it's a multi-fx module but it seems to be really suitable for hard techno as it has filter, delay, reverb, compressor and distortion. This can be used pretty good for those rumble kicks I think.

I removed the effect I had and added the one you suggested. Do I need an FX Aid Pro as well?

Both the Erica Synths Bassline and the x0x heart are quite similar - both have a saw/square VCO (bassline has also triangle tho), a filter that can do acid-type resonance, a gated VCA, accent input and VCF envelope depth. Unless you have a specific feature that you want on either of these machines, having them both seems a bit overkill.

They're both kits I have wanted to build for ages and had always been at the heart of what i planned to do so want to keep these

If you are interested in the possibilities of eurorack though, I'd remove either the Erica Synths Bassline or x0x heart and add the following modules:
- A separate VCA where you can control both the input signal AND the CV input signal (the Befaco Hexmix seems to do only of the combined output of the signal and CV in). Something like the Doepfer A-130-2 or the Happy Nerding 3x VCA. These give more flexibility to use the VCAs as simple attentuators as well. Maybe even more than 3 VCAs

I added a Doepfer Quad VCA. Will 4 be enough or should I add another?

  • As a sound source it'd be nice to use more dissonant or richter harmonic sounds as well. An analog VCO (which usually has saw, square, triangle and sine) is nice as base or a sub sound but it'd look into modules that can do a wider variety of sounds. These are more difficult to learn but give you more flexibility. A Mutable Intruments Plaits is often mentioned for this. Since the module is discontinued, you can also use clones

will have a look at this

  • Something that creates envelopes, LFOs, random, i.e. modulation.

Isn't this what Maths does?