Oven Issues

It was in the midst of having to bake two cakes for Ethan's birthday when I realized our oven wasn't working right.  So we went out and bought one of those oven thermometer only to find out that it was off by 100 degrees.  That's a big deal!  Wow, instantly so many dishes that literally flopped came to mind...and why.  You think I would have learned from our previous experience, but I didn't.  Then it got worse.  It would take about 30-45 minutes to preheat the oven just to get it to 350, which meant I really had to plan dinner WAY ahead of time.  Ha, thankfully we knew that ahead of time going into Thanksgiving.  Anyway, the landlord finally sent someone out to fix it but since he couldn't he brought a different/newer one.  Never mind it was three months later.  Now it preheats and maintains the temp great.  But then I ran into a different issue where everything was getting overcooked including my Chicken Enchilada dinner and Nuetella cupcakes the other night.  Then it dawn on us that it's a convection oven which apparently, you have to adjust either your temp or your cooking time.  Never knew that.  Ah, the frustration of cooking with someone else's appliance.  Well I will be a great cook/baker one of these days...if I can get all these ovens figured out.