Here's a great article to help you practice your pronunciation and to get the "flow" of the language (especially the ん sound and the little っ pauses): https://www.italki.com/article/754/Quick-Fix:-Make-Your-Pronunciation-Sound-Like-A-Native-Japanese I found #4 to be especially useful for me! Please message me if you have any more questions! I hope this helped.

For small っ there will be a pause(like-つかった-tsukatta).but if you use capital つ then it will pronounced as tsu.its doesn't depend wheter it is before a constant or not (like-つかう-tsukau).you can check other examples.

Yes, I find it helpful to think of a small っ like a pause in the middle, so だった is like dat-ta.