i have a brz1700.1 powering a 15" Fi BL fully loaded, and ill be adding a 4ch. soon for my 6 1/2 and 6x9's..my stock alt is 105amps and i have a stock battery.. will i need to get a new alt and battery???.. or do yall think ill be just fine with what i have already??? the system isnt installed yet still waiting on a few things to in...?

Hard to tell. I would at least upgrade the battery and go from there once everything is installed.

Upgraded battery and big 3 with proper wiring to amplifiers is a good start.

Upgrading your stock battery would be a great start. I have an 130a stock alt and stock but big battery with an 1200watt amp and I was doing fine for the first 5-7 weeks. Just now am I starting to notice any light dimming. I would suggest also to invest in a volt meter, which can be found via ebay for about 20$. Once you have that, then you will have a better understanding of how your vehicle is handling the extra stress. If you can afford it, also by an additional 10ft of 1/0 cable for the big 3 upgrade. Though maybe not needed, it always makes an great addition for down the road once you upgrade.

Upgrading your stock battery would be a great start. I have an 130a stock alt and stock but big battery with an 1200watt amp and I was doing fine for the first 5-7 weeks. Just now am I starting to notice any light dimming. I would suggest also to invest in a volt meter, which can be found via ebay for about 20$. Once you have that, then you will have a better understanding of how your vehicle is handling the extra stress. If you can afford it, also by an additional 10ft of 1/0 cable for the big 3 upgrade. Though maybe not needed, it always makes an great addition for down the road once you upgrade.

Yeah, in most cases (less than 2000 watts) just the Big 3 upgrade and a better performing battery will do.

im running a brz1200 on a 15" Q and with 0 ga to amp i had serious dimming, need to get big 3 done but I did upgrade front bat and that helped alot, i would reccomend a bigger battery first...and get the biggest that you can fit and afford...im wishing i got a bigger battery!! just my 2 cents!!