Looks like you have a plan. I bought a Pittsburgh Micro Sequencer. I hate it, personally. I find that accessing features to be really unintuitive. If your budget allows, try a micro Ornaments & Crime. They are 8HP... 2HP less than the Micro. The menuing system is much easier to navigate than the frustrating button combinations on the Micro. A Micro will cost you around $160-$200. The O_C is about $250-$275. If you go with a larger format O_C you can get them for about $200.
An alternative to the Happy Nerding Mutes is the Joranalogue Switch 4. It's $20 more but includes more features. Each of the four switches come with a three-way toggle (momentary, off, and on). Plus there are two additional outputs connected to two rotary switches with an on/off switch as well. It's a little bigger than the Happy Nerding Mutes but the additional features are worth it in my opinion.
You may also have an issue finding Happy Nerding stuff in North America.
Additionally, the 2HP bell... have you thought about a micro Braids module instead? It'll cover bell sounds as well as a host of other sounds. It's probably double the cost and roughly 10HP in width. But you'll get a lot more out of the module.
Another possibility to add more oscillators is a Behringer Model D and leave it in its original case. It has a Eurorack jacks built into it and includes a 1V/Octave input plus a jack out of the mixer section. That gives you a three oscillator stack plus noise for $300... plus a Mini-Moog clone. Lugia despises Behringer. But I find the cost benefit and the sound to be well worth it. $0.02.