This seems like a question that has probably been answered, but I am not finding it here:

Once you get through training, IOE, etc, and start at your first base, how often and how hard is it to change bases? It seems like bids are monthly, is it realistic to try out a new base after a month or two? Or are there any barriers to such movement? Or other downsides? Thanks.

They process bids every month and if there is an opening and your seniority can hold it, you will be awarded it. You could change bases every month if you wanted to and had the seniority. But after IOE there are only a couple bases that you can hold then anyway.

For reference, I was in 3 different bases in 4 months during and after IOE. But keep in mind that you might be finishing up a trip in one base on the 31st, and then have another trip in the new base 2 days later.

It's all based on seniority. Once you're around for a little bit you'll Learn how to use SWOL too.

You'll be able to check the domicile vacancy report and the Standing bid list to see where you stand.