If you have no knowledge of VBA... I'd avoid building such application in Excel.
While VBA is relatively easy to code and learn, it doesn't have good error handling and logging feature.
Also, Excel is great at flexible data handling, but it isn't well suited for managing data integrity and security.
I'd recommend investing time and/or money in researching for proper POS/CRM database. Trust me, it will make your life so much easier down the line.
There are plenty of Open Source software out there. Such as VTiger, SuiteCRM etc.
Or use cloud service, if you don't have time to invest in building your own application or server. There are plenty of cheap options out there (from around $10US/month).
I haven't used it personally, but Bitrix24 seems pretty good. CRM feature with built in invoicing/asset management. Free for up to 12 users, 1 admin and 5gb of online storage.