Sign him. He is 30, and the max I'd do is 6.0/6.5.
The cap has been allocated for those asking just with the subtraction of Perron and Lovejoy, and there are contracts up as soon as the end of next season. Even with needing to re-sign Maatta and others room will be there for it.
You wanted the youth and there will be in the forward and defensive positions.
The cap is not my concern at all.
So you want to move Pouliot + Perron (and maybe Lovejoy) for Buff.
That trade is terrible value-wise and asset-wise for the Pens.
Then you want to sign Buff to term at 6-6.5M.
Lovejoy's contract if he is involved doesn't matter. The Pens were already going to struggle to sign Maatta & Perron. Buff is going to ask for more than Perron. Lovejoy (1.1) + Pouliot (0.9) + Perron (3.8) + cap rising (2) = covers Buff @ 6.5M + 1.3M for Maatta. Pens need additional space for Maatta and Perron's replacement. The cap does matter & is an issue.
Your contract also doesn't include term. How long is Buff's new contract?
Also, what youth is on the blueline? 2016-17 Buff will be 31, Letang 29, Cole 27, Dumoulin 25, Scuderi 37. Maatta & maybe Clendening?
In short, I am glad you are not the GM.