Well as I recall there are 23 R's up this time and there are only 2 D's who are viewed to be really at risk Doug Jones in AL it is an uphill climb, the other slips my mind at this moment.
There are factors that will make all the difference
Candidate selection will matter
Turnout will be critical
A few R-s where it is at best 50/50
Susan Collins, BK has already made her look like naive deluded fool by ALREADY "not respecting precedent" as she assured everyone he WOULD If between now and next November one of these cases such as the recently passed and even more recently struck down by a Federal judge MS "fetal heartbeat" abortion ban makes it before the SC and he votes on the side to have it upheld or at a minimum he votes to have it heard she can claim until the cows come home that he was not voting to actually "overturn Roe v Wade" and her goose will be cooked
Pat Toomey He has lucked up twice in the opponent he had and when he ran but based on how things went in PA in 2018 he could loose for sure
Corey Gardner, he is the rock mountain version of Pat Toomey but even worse, he can not even claim the Trump won the state in 2016
Tom Tillis The pendulum is swinging back in NC , a year out everyone said that Pat McCorey could not be beat well he did get beat and it was not all that close. Even though Trump won the state in 2018 it was by no means a blowout If the Democrat wins the state as President Obama did he looses, the days of "ticket splitting are OVER
Arizona, Mark Kelly the astronaut has good shot, better than 50/50
TX, TN and KY it depends on the candidate, candidates in the case of TN and turnout but none are slam dunks like you would think.
Even MS is not as safe as you would think, CHS is running again and it could come down to turnout. The AG who is Democrat and has won statewide as AG for as long as I can remember is running for Governor if he manages to win then that could show the path to beating her
So a gain of 3 seems well within reach 13 or 14 would take "blue wave" but we have already seen that happen so it is not all that impossible but even if he does not get there Chuck Schumer will not fuck around and "negotiate" with Mitch McConnell (assuming he is still there) the way Harry Reid did. He will tell good old Mitch to go fuck himself, and go nuclear all the way in order to get things done or at the very least make "filibustering" way harder to do than it is now and worry about what may result from that later