It may be worth getting a Disting EX. The EX is a little more expensive than two mk4's and is less "eurorack-y" but it is far more usable than the mk4 and it is just a very flexible module. Some things I like using the EX for is as a wavetable sound source, a mono-to-stereo reverb, a compressor, a precession adder, and as a clockable AD envelope.
If you are looking for a random cv/gate generator a good one to look at is the Clank Chaos. It has 6 channels of gates and cv with the ability to go from very random to a repeating loop and it has a variety of additional useful features such as slew and quantize capabilities. If you want to make percussive sounds you should look at Rings. I find Rings very useful for as a type of accent tool, for lack of a better term. It is not uncommon for my patches to have audio be split to Rings and have the accent/reset of one of my sequencers ping Rings. If you are looking for envelopes the Behringer 140 is a solid option. It may be a bit too much HP-wise but you get two independent ADSRs with two normal outs from each ADSR and an inverted out. It also comes with a solid LFO. I have never tried this but I do believe you can use the LFO of the 140 as a basic waveform oscillator too via its frequency CV in.
If you want to have more tactile control over the gates you are using you can take a Grids and use it in the gate mode. This allows you to control the frequency of the gates and how many there are using your hands. This can go well with a swing module so that the clock that it receives leads to not completely on the grid notes. Something I would recommend, especially if you do go this rout, is to get some type of fader bank. I use MSW's but I know they aren't the only ones who make this. Having faders outside of the case that can control things can make modulation much easier, especially if you are using Grids like this.