In my response below, I'm addressing these topics from the perspective of someone who used to like some of the high level messaging of the Republican Party many years ago, but then realized that the world is changing drastically and that many of the messages put forth by the Republican Party have been disengenuous. In addition, I've also started sharply questioning the basic ideas we hear in the media, because they are driven by progaganda in many cases and not facts. So here we go:
Packing the Supreme Court - several others have already pointed out that the only ones really doing it right now and trying to do it are Republicans. Yes, extreme parts of the left have discussed this. But being a staunch Republican doesn't fix this issue given what Republicans have been doing, so how can this make you feel better as a Republican?
Eliminating the Senate - as several others have said, this is a viewpoint from extremists. So why are you fearful of these extremists and not extreme Republicans, or Republicans on the payroll of Russia, or Republicans who cater to white supremicists? We had a President and group of Republicans literally try to eliminate the Excecutive branch as a voting decision. Shouldn't your concern here cause you to distrust both parties and want to support people who have the right moral integrity and are moderate, regardless of party?
Changing to Popular Vote - This is a decent topic for people to argue over. While on one hand you can make the argument that popular vote should be the rule, there is an equal counter-argument that preserving a minority population's (small state) ability to have control over how they live in the US is an important protected right. If this item is really that important to you, then this might be a decent reason to align right.
Medicare For All - I agree that totally run government healthcare may not be the right answer. It comes down to the fact that companies have way more bargaining power than individuals. If we had Medicare for all, there might not be a sufficient governor on costs, like there is with competition. The winning strategy needs to be some sort of combination of multiple ideas that ensures competition but also efficiency. But how can you be Republican because of your opposition to this? The Republicans have offered NOTHING for a decade in terms of an idea. Hell, they even controlled both houses and the Presidency and DID NOTHING. Nothing doesn't deserve support or a vote. Get moderates from both parties.
Wealth Tax - I probably differ from almost everyone on this topic in supporting some sort of wealth tax but not in the currently envisioned model of Elizabeth Warren. Why? Envision the middle ages when the wealthy had so much control of land, resources and wealth that the rest of the population was living as serfs. The wealth inequality changes we are now facing as a world are becoming so large, the risk of the 90-99% never being able to live a decent life is a real future threat. The amount of money in a small number of people's hands is stunning. So I don't understand why so many are against this idea given the impact on the 90-99%. And being a Republican for just this issue seems crazy. The billionaires don't need your help to make their lives awesome. Why align with them?
Tax Increases for $1-2M couples - This is where your logic really runs aground. As Sydney and others have said, right now the Republicans are cutting taxes, but driving up massive deficits, but only wanting to cut spending in areas that hurt people making under $1M. The Republicans are protecting everyone OVER $1-2M. Again, why are you wanting to help the $50-100M aires and billionaires, but not yourself and the majority of the population? This is a classic example of listening to Republican party rhetoric but not understanding they are pulling money out of your back pocket while you salute the flag.
Estate Taxes as is - While $25M is pretty high, dropping it to $6M is bullshit. But again, why align with Republicans? The right answer is probably $15-25M for now. But Republicans want to remove it completely for their ultra-rich donors who have Republicans on their payrolls. So why in the world support that? Can't we find a mix of Republican and Democrat moderates that set it at $15-20M?
EV Conversion Mandates - There are some open issues here. But again, what in the world are Republicans doing to help this transition over the next 20 years? Nothing. They just are trying to advocate for the interests of their wealthy energy donors. So why are you aligning with people on the take from energy donors?
Hydroelectric Dams - This is a nonsense red herring. Moderates on both sides of the aisle can make the right choices here.
So in summary, some of your topics of concern are valid, but what I've realized over the last 10 years is that not only will the Republican party not address any of them, their major focus is on padding their own bank accounts from the wealthy, who are trying to use them to stay wealthy and get wealthier. Why align with that? I'd rather align with whoever is moderate to solve real problems for the 90-99%.