Not much to add, only you should consider balance when setting up your rig. A chest rig only loads on the front, so all extra weight will be up front. This is great if you only have about 6 large mags, the odd smoke or spare bag of ammo to put in the rig, and any extra goes elsewhere. There is nothing in the rear to counterbalance the weight. Depending on how high you are wearing the rig, you should also consider how this bulk will be carried when you are prone or if it will interfere with bringing the gun up to the correct aiming position.
If you have a PC, you will probably load closer to the waist area, and you can counterbalance extra weight on the front with rear mounted utilities or MOLLE mounted hydration. It will also distribute weight across the back via a wider surface area than chest rig strapping if you shift from upright to prone. If you are planning on a field kit of 8-12 large mags, dump bag, hydration and spare ammo/batteries (some sites make you hike out for the afternoon and you 'fight your way back', so you won't make it back to the safe zone until time to go home), you should consider a PC in preference to a chest rig. If you are purchasing a PC, you may wish to consider if it has structural stability built in (if it doesn't have a plate in it, does it flop about like fabric, or does it maintain most of its shape) as structural stability is quite important in MOLLE gear for pouches and gear not to sag and shift about when worn.
I'm not too much in favour of chest rigs that have rear panels. If you want a chest rig, get a chest rig. If you want a vest, get a vest. Each design has its advantages and disadvantages, and making an add-on to turn a chest rig into a halfway vest isn't going to make the chest rig more viable as a vest due to issue of balancing out the weight. Chest rigs are great add-ons to standard armour or webbing for adding extra ammo carrying capacity (in military/LE applications), and the wearers already have a counterbalance to the load in the armour, utility pouches on the rear of the webbing or a rucksack/daypack.
If you still aren't sure, a modular web set combined with a jacket with lots of pockets is a great way to go. 8-12 large mags in pouches around the hips, a dump bag or utility bag slung on one side for empties, all arranged for the balance to be neutral. Other spares distributed on the body in the jacket (would suggest a pouch that will carry an extra bag of BBs to go into the pocket in case the bag opens up - will also prevent the BBs from getting dirty or damp if you find yourself crawling on damp ground for an extended period of time. This is fairly foolproof and a cheap way to start off until you are sure you want to carry more stuff.