If purchasing and holding, is a node necessary?

Just a preface, I want to set up my Bitcoin to be secure as possible, so looking into a node. My goal is to purchase bitcoin, hold it then sell a portion of it in 15 years. Unless there’s an apocalyptic event, I don’t want to transact during this period.

If all I’m doing is purchasing, holding, then eventually selling and crediting my fiat bank account, does a node provide more security for this process?

Also, I see you can get a closed source node such as the Start 9 Server One, or an open source such as the Start 9 Pure. It looks like the Start 9 Pure will further future proof any security risks as it’s open source. If all I’m doing is purchasing holding, then eventually selling, and will not be running anything else on the server, is there any advantage or point in getting the Start 9 Pure?