Its a super budget ghetto stylee box.. There's a saying that goes 'You only get out - what you put in' and that stands true with most things, on the positive side ur already aware 'Tin-foil' is a no no...so I am surprised you bothered with it. However, despite the slightly bigger box, That CFL fixture is huge ~ (for a single low-Watt CFL)!! ..and so I'd expect a Micro sized dwarf plant is how it'll go. You could put a small SCROG screen in there which will allow you to obtain a fair bit of extra 'Bud' gain, But I'd wanna sort out Mylar/Orca for the reflective surfacing 1st, then I'd replace that shoddy CFL setup you have in exchange for a single ENVIROLITE 125W CFL which will not only save you space, (if hung horizontally) But also give a much better PAR/Usable light output, & also not give off as much heat as say a small HID setup ie: 35W, 70W 150W ... I think a 250W Son-T HPS would be overkill for the box you have .. I take it your fine with smell etc.. only I dont see a Carbon Filter?!! and even if there was one I am pretty sure the smell would still leak out!
Still its your grow and I am interested to see this Ghetto-Grow get on the way.. Please keep adding pics I hope my helpful criticism was helpful as intended and you didn't/don't feel I was rippin on you.. Its funny though, loads of people start out like this or in a very similar way (inc me) and slowly after each Harvest improvements are made and slowly the small box turns into a good sized Grow-Room or Cab.. Best of luck I look forward to seeing what further mods you make to this box.. I hope it goes well for ya!

- STELTHY