I'm very much pro EU, and I don't want to deviate from the OP's excellent original article too much, but here are few Belgium specific examples. Not too many of them hold for all EU member states, but those would still make for significant hurdles:

- You need to formally set up as a company. Where are you going to do so?

  - Not allowed from student housing.

  - If your parents rent their home, their rental contract usually forbids this.  It would cause the landlord significant taxation issues, so almost all rental contracts forbid this.

- Establishing the simplest allowable entity able to send invoices. Just establishing would cost ~115€, or ~134€. The article student author mentions $100 being a lot of money to them.

- Provincial tax. Most Belgian provinces have a yearly tax on the existence of any company, no matter how small or inactive. My native province's rate for example is 140€. That's ~$163 at today's rate.

- Local tax. Many local governments tax business activity separately.

- Social security.

  - Registration and exemption documents. No cost, but an added significant administrative burden to prove you are in the exempt bracket for your first ~2000€ earned.

  - Work too many hours or earn too much. Your parents risk losing your child benefits. Note that this is separate from dependent deductions. What if money is tight for them?

- Peppol electronic invoicing. If you buy or sell anything b2b, you're required to use the peppol electronic invoicing network. No self made pdf's allowed. Set up software. Pay for a subscription.

- Banking. Better get a separate bank account for your business, or you give fiscal authorities the right to start looking into your private accounts.

- Fiscal uncanny valley. Combine any regular tech job with a sole proprietorship side gig. You pay ~53.5% in income taxes and ~21% in social security contributions on the net side income, keeping about 1/3 of your net taxable income.

- VAT and administration. Have you seriously tried to sell across intra-EU borders as a student and stay compliant?

  - Hope you didn't use Amazon FBA or any 3PL partner in a different EU country.

  - I just imported a single camera module from China. It cost $49 including shipping. 21% EU import VAT and administrative handling by the national post monopoly combined cost me 35.17€, or $40.93 on top.

  - Forget about doing your first year accounts yourself. You'll make costly mistakes. The tax administration doesn't bark. It bites. Do you have the cash to outsource trimonthly VAT declarations and income tax accounting? Good luck finding someone competent under 1k€/~$1163.

- Earn over a relatively low token amount. If you're from a family with 3+ kids, your parents risk losing a 3k€+ net tax advantage. This can in some cases make for a significantly >100% taxation rate between parents and student children. What if your parents can't afford the tax increase?

- Student status. Drop below 27 ECTS points of course load and you're not a student entrepreneur anymore. You're suddenly a full-time entrepreneur, with the full load of responsibilities. Example: 3.6k€/year in social security contributions, even on zero or negative income. Where are you going to get the money?

- Physical product.

  - Belgium has some of the highest outgoing shipping rates across any courier or postal services. Good luck competing against similar initiatives, including from other EU member states.

  - Electronics specific. CE compliance is expensive. It also requires your product to have accompanying notes in the language of the EU country where you sell.