How do I start keeping the Sabbath and the feasts practically?

If you are asking how to begin, you have already made the real decision, and the only thing left is the doing. So hear this first: you do not have to feel ready, and you do not have to do it perfectly. This is a walk, not a license exam. Nobody grades the first step.

Start with Shabbat, the Sabbath, and start this week. The Hebrew day runs from sunset to sunset, evening then morning, the rhythm Genesis sets from the very first day (Genesis 1:5). So pick this Friday evening through Saturday evening. When the sun goes down Friday, stop your work, the way the command actually reads: remember the Sabbath day, to keep it holy, and do no work (Exodus 20:8-10). Then make it warm and real. Share a meal. Light a candle if you like. Put the phone down. Rest your body, rest your striving, be with the people you love. That is most of it. You are not performing; you are receiving a gift HaShem built into the world and then blessed and set apart (Genesis 2:3).

Then take the feasts one at a time, as they arrive. Do not try to swallow the whole calendar at once. When the next appointed time comes around, open Leviticus 23, the chapter where HaShem lists His mo'edim, His set-apart times, and simply read what it says about that one feast. Then keep it simply, at the level you can actually do this year. A simple Passover meal. A real rest on the day He names. Next year you add a little. The point is to begin walking the calendar God keeps, not to master it in a season.

Go to the text for the next step, not to a teacher's rulebook. Read Leviticus 23 straight through once so you can see the shape of the year, then come back to whichever feast is closest on the calendar and let the verses tell you what to do. Start small, start now, and let the rhythm teach you as you go.