Great question!
Yismach yisroel is very uplifting; you can skip the kabalah parts. It always puts a smile on my face. Divrei yoel is one of my favorite drush seforim; the satmar rov builds up a massive edifice in each shtikel. Sfas emes is very open ended; they call it a “mirror” wherein you see the Expression of your neshoma in the way you understand it. rav gedalya schorr”s oldest son rav yitzchok meir schorr told me that the later years are easier. The 2nd half of the tanya is very good for understanding the chasidish approach to avodas Hashem and it’s among the more organized chasidish seforim; those perakim are referred to as the “poilisher prakim”, because post kotzk polish chasidus was not very into theoretical kabalah discussion.
I’d also recommend learning nefesh hachaim at the same time to get a balanced view.