1. Definitely add some
Lavalock gasket - that's way too much leaking IMHO.
2. Restricting airflow isn't recommended for reasons already mentioned, but can also lead to acrid tasting meat if you're not careful.
3. I see that you do add
some chunks via the smoke tube and smoke box. That's the biggest difference with the SD - you have to rely on pellets in smoke tubes, which do not burn the same as actual chunks of wood (which is very easy to feed into the SD). On the SD, most of us are 100% wood chunks and actual wood chips - which have a far more robust smoke than any pellet can deliver. As a reminder, all pellets - no matter what any manufacturer says - are just compressed sawdust. Wood chunks/chips have solid lignin and a far greater variety of "parts" (including bark, etc). Your smoke is going to be far closer to a stick burner.
So the short of it is: if you think the smoke taste you're getting from a smoke tube/box is good, a SD (burning only chunks and chips) is
better.
Of course YMMV... maybe you won't even taste a difference. And if you or your family prefers mild smoke, it might be best for you to stick to your approach. SD's profile are much closer to stick burners, which some say is too harsh - especially if all you've ever tasted is pellet smoker cooks.