Even if startup founders had time to spare spending a month learning how to doing each and every task they needed to hire for (and trading money they have for time they don't is the whole point of hiring) they'd (i) have no time left to focus on the core business (ii) do a really bad job and (iii) having barely understood the basics, run exactly the same risk of hiring good interviewees with the right credentials that were actually bad at their jobs. Maybe they'd even be more sympathetic to the bad hire because well, he's better than I was
That’s not to say I disagree with your points in general, but just that hiring is every bit as much of a minefield as doing things yourself. In either case you have to understand what is most crucial for the next stage of growth and prune everything else obsessively.
If you're really motivated to participate in x you should try, if you're a bootstrapping solopreneur you may have no choice, but if you're looking at mitigating hiring risk, a month trying to code/sell/design outside your comfort zone doesn't really move the needle on figuring out how to evaluate programmers or whether your startup actually needs a sales team. (If anything, you're more likely to get the wrong answers from the DIY approach because maybe the sales function actually would be beneficial if it was carried out by someone who could sell...).
That's where you get more insight in less time from leaning on people in your network who actually are marketers or salespeople or product people to get a view, especially if they're not financially incentivised to propose a particular route.
If you want to mitigate the risk that ICs need structure and resources, you focus your hiring on candidates that have worked without structure and resources. But even having a codebase written by someone learning not to rely on Scrum meetings and JIRA tickets to prioritise is still better than having one written by someone learning to code.
When I started my business (non-tech), i knew very little about sales processes or relationship building from a sales perspective. One of my first consistent customers (disclosure: he is also a close friend) is a sales professional. I learned the very basics of sales, and came to him, asking what were probably dumb or basic questions, but he was more than happy to answer them and also point out where, as the company grew (and hopefully grows!), what to look for in sales people and relationship managers. While I still know little in comparison to him, I know some of the right questions to ask, what to expect from those questions, and what sorts of answers I should be looking for. He also knows that I can call him with deeper questions and to help me evaluate a sales-related situation as it arises, and he'll give me a no bullshit honest answer.
Find people like that.
