Hi Mate, Few little things to address here. Occasionly the Shop tablet can bug out and become invisible (Only to you) When this happens either try re-logging, If the issue persists just delete your mission file and re-download when joining the server.
Arma3 is a buggy game by nature, Especially when scripts are introduced. A general rule of thumb is to not jump so close to a wall because you will get stuck, float and either come out dead or injured (Just dont jump for no reason and you'll be fine)
Not really sure what you mean by the text messages..
15k may seem like alot now when you just start out, But progression on Darkside works with a snowball effect. The more time you invest into The Darkside, the easier it becomes to obtain money (Eg. Truck missions are a big helper, Initial grind and then youre set with a stable income past that, Real estate etc)
If you have blown all your money dying to glitches etc , Send me a message if you see me ingame and i can help get you started (If you really have hit rock-bottom)
Ultimately your best bet is the Civ questline and truck missions.