The main activity of Czech company would be buying colored metals. Is it possible to add other activities later and what are the costs?

All available activities are registered for all Czech companies, therefore, there is no option to add business activities or scope, because the company has them all, with the exception of regulated activities (hairdresser, air-travel and similar).

The two owners would be from Slovenia, what kind of taxes would they need to pay in Czech?

Owners of Czech company do not pay any tax in Czechia unless they pay out dividends.

What is taxation of profits?

Corporate tax rate in the Czech Republic is 19%.

The monthly turnover of the newly established company is estimated at 30,000-40,000 € per month. The company will do business with Slovakia, Austria … are there any restrictions with non-EU countries?

There are many sanction on business with Russia, there are tariffs and quotas applied to trade of goods with non-EU countries.

What is the procedure regarding the possible closure of the company? Are there any special conditions?

The liquidation of a Czech company takes about 7 months and the company must provide evidence that it does not own any assets or liabilities.

How are dividends taxed?

Dividends paid to residents and non-residents are subject to 15% withholding tax in Czech Republic. 
Dividends paid from a subsidiary (CZ, EU) to its parent company (CZ, EU) are exempted from taxation, if the parent holds at least a 10% share in the subsidiary for at least 12 uninterrupted months.
Withholding tax of 35% applies when dividends are paid to other jurisdictions than EU/EEA states or states with which the Czech Republic did not conclude a double tax treaty.

What is the tax rate for profits?

Corporate income tax rate is 19% in Czech Republic.

The annual profit of the newly established company is estimated at 30,000-40,000 €. Monthly traffic is estimated at approx. 100.000-150.000 €. The company will do business with Slovakia, Austria, Slovenia and Italy … are there any restrictions?

There are tariffs and quotas on trade with non-EU countries and sanction for Russian and other entities.

The company will buy and registered cars in Czech Republic. It si better to input bigger share capital for buying cars? What are the restrictions or taxation and use? Is the virtual office in this case a problem?

No special share capital requirement for buying cars. 

Virtual office is generally not a problem for buying cars.

Have any subsidies been issued for newly established companies in the Czech Republic?

There are no subsidies for new companies in Czech Republic unless applied for in a costly process.

How quickly company can be set up and ready to start business?

Company can be set up within 10 days from payment and delivery of signed documents.