1C - this is as if we doubled 1C, so the idea here would be either a 3-suited hand, short in clubs OR a strong hand (17+ points, typically).
1D/1H/1S - 8-16 points, natural suit (good quality, maybe 4 cards)
1NT - 12-14 HCP, balanced. You want to change this from 15-18 so that you and your partner don't pass out two 13 point balanced hands across from each other (that's a missed game! How embarrassing...)
2C - This is like a Michael's Cuebid showing the majors. It could be weak or strong, but with intermediate hands (11-15 points or so), I would open one of the majors and then bid the other if given the chance.
2D/2H/2S - Weak, 6-card suits (like standard)
2NT - I would play this as a 2-suited hand in the minor suits. Normally, it would be an Unusual 2NT showing the 2 lowest unbid suits, but that wouldn't be as useful as having a bid for the minors that is this destructive!
3 suit - Preemptive
3NT - To play. You could play this as a Gambling 3NT if you want, though.
That's it! The only comments I would make on this system is that you and your partner need to be on the same page about what to do as overcallers (since now you are always overcallers), and that the responses and rebids to the 1C opening should be discussed in detail (1C is the easiest bid for the opponents to overcall). For example,
Responses to 1C: NO PASS! Normally you could pass a takeout double of 1C, but you might miss a game if you do in this case.
1D/1H/1S = 0-7 pts, 4 card suit (could be as short as 3)
1NT = 7-10 pts, balanced
2C = 12+ pts, any shape
2D/2H/2S = 8-11 pts, 4 card suit
2NT = 11-13 pts, balanced
Opener will rebid a new suit, or "cuebid" clubs again with a stronger hand (21+ pts).
With interference over 1C, responder would pass with 0-7 pts, bid something with 8-11 pts, and cuebid the most recent opponent bid to show a game-forcing hand.
Alright, you probably get the idea by now. Obviously, you should use the bids you and your partner already use in competition, asking yourselves questions like, "Are responses to 1 suit forcing or non-forcing?" or "how do I show a game-forcing raise of 1M?" By the way, if you play in an ACBL-sanctioned event with this system, I wouldn't recommend opening with less than 8 points. Plus, you need to mark on your convention card that you play very light openings. Happy bidding!