My early kit going into gold was the Salarian Infiltrator with the Mantis X. Energy Drain was a life saver, but times have also changed a lot since that time (Dragoons, more turrets on wave 7, Atlas DoT, etc.) and it would definitely be rougher to jump in with that. My suggestion would be the Geth Infiltrator with the Geth Plasma Shotgun honestly. Regardless of what people say about "crutches" you have to start somewhere and the GI is one of the best kits for learning the ropes since Hunter Mode gives you a lot more awareness, but mistakes are also costly with the low health/shields. You can also learn spawn points a lot easier with it which helps with survival.
Quarian Male Engineer is another kit that is just an absolute monster once you have Grenade Capacity up some. I honestly don't even use it that much anymore because I feel way too ridiculous using it, but for someone starting out in gold it is definitely a solid choice with Arc Grenade/Incinerate combos. Also, at this stage of the game you have to expect to be "carried" on occasion on gold. A lot of people have far more experience and will just run things over as second nature, which can leave someone new in a bind as they aren't going to know when a spawn is going to pop up right by them, causing them quite a few deaths. My suggestion would be that if that happens, just watch someone that is good if you end up in spectator mode and learn from what they do. You will see a lot of right hand advantage, kiting when necessary, and notice them kind of "feel" the enemies flanking them.
I personally wouldn't suggest going the AIU/TGI route since I feel that teaches bad habits since you can't always rely on free ops packs/medi-gels in stim packs or repair matrix, but that is your choice to make if you want to go that route. Experience will be your best teacher, so watch some gameplay on youtube of some of the better players to get a feel for things and then just jump in and give it a shot. The worst that can happen is you don't do well and you try again next time, or you could do fairly well for what you have and build up more confidence. Maybe add some BSNers willing to show you the ropes if possible, I know even when I was "carrying" gold games early on I still had a lot to learn and didn't become a really good player until players better than myself gave me a lot of advice/information.