Having a separate Semantic model or using semantic model from warehouse or lakehouse is suggested

Hi anusha_2023 yes there is a "default" semantic model that is created when a lakehouse or warehouse is created.  Plus you can create a custom semantic model in the service itself.  At the moment it seems like you are importing into your semantic model.

In terms of options, yes you can use the default semantic model or create a custom semantic model in the service and this opens up the option to use DirectLake - this is the storage mode where you don't need to import data into a semantic model as it offers almost import-like performance.  You can use this mode with Lakehouses and Warehouses.  However there are caveats to using this storage mode: Learn about Direct Lake in Power BI and Microsoft Fabric - Power BI | Microsoft Learn

You can also model/edit your semantic model using Tabular Editor which will still allow Direct Lake Editing your Direct Lake Datasets from Tabular Editor? Yes please! - YouTube

At the moment you can't create a new semantic model using Power BI Desktop natively and publish to the service and enable Direct Lake, hopefully this will be supported soon.  Please read the  "Model write support with XMLA endpoint" to view the options in terms of deploying models to the service which can support DirectLake mode. Learn about Direct Lake in Power BI and Microsoft Fabric - Power BI | Microsoft Learn

In terms of your questions:

1. You can avoid scheduling a semantic model refresh by using DirectLake (please see DirectLake article above and take care to look at the limitations)

2. Yes you can create multiple semantic models using the same warehouse or lakehouse