an IRA is an individual retirement account.
a solo 401k is an employer sponsored retirement account
they really have nothing to do with one another. You can have both.
you can contribute to an IRA if you have earned income. It seems that you do. There are annual contribution limits depending on age, and whether you can deduct a traditional IRA contribution, or contribute directly to a Roth IRA, depends on your income level.
as a sole proprietor, you are employer and employee. You can establish a solo 401k. Money can get into the solo 401k from the employee (salary deferral) and/or the employer (profit sharing). You could do either or both. Again, there are limits. A solo 401k plan is more complex than an IRA and you can create a mess if you don't understand what you're doing. You want to be careful to never over-contribute.
With $8000 of sole proprietorship income you could contribute almost all of this as elective employee salary deferral to a solo 401k. But then, because you've deferred your salary, you no longer have earned income. So, you could not contribute to an IRA.
Alternatively, you could make a lesser elective salary deferral to the solo 401k. Then, you would still have some earned income, and could contribute to an IRA. And because there is still business profit, you could also make an employer profit sharing contribution to the solo 401k. There is interplay between all these numbers and it would take some work to figure out what is best in your personal situation.
The point is, you should probably not do anything until you have a good understanding of what you're doing. Certainly this is the case with a solo 401k.
What is your adjusted gross income? What is your marginal tax rate?