No worries, I shall go through things in order as you posted
1) Yes the background music is fine, maybe turn it down a little as sometimes it can be a little distracting, especially in your latetst video arounf the 4.40 mark I belive the background noise skyrocketed for some reason and it was a bit surprising
2) I would always say have a quick, no more than 6 second, intro as this can be a gateway into your videos and really help you stand out from other users
3) I'm not sure if appealing is the right word, I don't mind it, all I would say is the name and banner doesn't really show me what your all about, and that is what you need - both your name and your channel info to mean something
4) Your thumbnails do look but again they don't really sell the videos - in that I mean I look at them and get the general idea what the video will be about but nothing overly grabs my attention. It might be worth looking at other Youtubers and getting an idea regarding thumbnails from them or searching for things that you have done, for example funny moments on GTA and Rocket League and taking inspiration from other people.
One side note I will mention, and this is on top of the review given above, is it might also be worth setting up a consistent update schedule, this could be once a month, once a fortnight or anything like that but be consistent. Also fill out information on your YT channel, such as the about page, tell us some info about your channel, what you do and as I said previously your schedule.
