I think your thinking is pretty much right on. It's something I've been saying for eons it seems.
Right now, Georgia seems to be only seat held by the Democrats that is in jeopardy. While the Republicans have three, two due to retirements, Pennsylvania and North Carolina along with Wisconsin where Johnson isn't liked much. The rest seems at this point, to be safe for which ever party who currently holds them. This translate into a 1-2 seat net gain for the democrats in the senate.
The house, who the heck knows. No district lines have been drawn yet. For the party that holds a trifecta, there are some tricks to drawing those lines. Placing two incumbents in the same district if the incumbents aren't of the trifecta's party is one use a lot. Open seats are much more easier to switch or win. Packing minorities into court ordered majority minority districts is another. there's other tricks of the trade.
Independents don't like either party's congressional critters, but they do like Biden. At least so far. But Biden may still be benefiting from not being Trump and behaving presidential and like an adult. with independents.
Cracks are there though, inflation, illegal immigration, foreign policy to name but three. Biden is also benefiting from COVID-19 response. This advantage may wane among independents as COVID begins to go away.
Foreign Policy - Biden has dropped from a high of 56% down to 49%
Immigration - Biden has dropped from 52% down to 39%
Economy - Biden has remained steady here at 53%. inflation hasn't hurt him yet.
Biden's overall job approval, from 56% down to 54%. still very good. Hence the word cracks.
I think the senate will remain in Democratic hands. the House ?????????????????