I basically agree with Scarblac.

However, if going for sharp main lines straight away seems daunting, 1.e4 is also quite flexible in the sense that the lines you play against each of Black's main defences are independent of each other. So you could start out with some relatively low-theory but sound side lines to get up and running quickly, and then add sharper main lines gradually on top of that base. Eventually you may have two choices against each major defense; being a bit unpredictable never hurts.

When I last played 1.e4 regularly, it was with just such a "sound, low theory sidelines" repertoire:
- Sicilian: Grand Prix Attack
- Bishop's game/Vienna game
- French Tarrasch (avoiding some of the sharpest, most theoretical lines within it)
- Caro-Kann: Short system
etc.

Just before I switched to other first moves, I was starting to upgrade with the Ruy Lopez and 2.Nf3/3.Bb5 Sicilians. Today I wouldn't have chosen the Grand Prix since it's probably not very good; likely c3 Sicilian or Bb5 Sicilians instead. Or even 1.e4 c5 2.b3 as advocated in the Sveshnikovs' "blitz repertoire" book. And the Short system has become a main line with reams of theory in the last decade, so it no longer fits.

But I still stand by the basic philosophy: First a quick basis, then add main lines. Of course you will probably go straight for Open Sicilians since you have a good feel for them.

I'm looking to get back into playing OTB after a 10 year break, and am somewhat confused about what openings I should take up (especially as white), as I never really had a proper repertoire before, and after 10 years I've forgotten the little I knew.

So, I'm 35 and haven't played OTB since 2006.  My last rating was ECF 155 (this was back before the grades were inflated circa 2009, so I don't know what that equates to in terms of FIDE rating, but I was easily holding my own against guys who had FIDE ratings of around 2000), although I'd only played a total of about 50 rated games over about 5 years, and I think I was still improving at the time, when I had to stop playing due to work leaving me no time in the evenings.  Now I have a less time consuming job, I'm looking to start playing again, with the intention of improving towards 200 ECF/2200 FIDE.  But for that, I realise, I'll need to know what I'm doing in the opening.

I never really had a proper opening repertoire, especially as white.  When I was a kid, I used to play the London System because I was oblivious to opening theory and those were the moves that came naturally to me.  I thought I was just following opening principles.  When I started playing at a club in my 20s, I drew too many games against weaker players, and the club's stronger players told me I needed to play open games, so I switched to 1.e4.  I never really had a proper repertoire, though, and most of the time I used to just swindle games from worse positions because I could out-calculate opponents 25+ years older than me, and my endgame play was always good for my rating level (which I'd ascribe to my ignorance of the existence of opening theory as a young player allowing me to work on other parts of my game).

Still, I played 1.e4 for most of my rated games, and tried to play in an aggressive attacking style.  Nowadays, I'm somewhat confused as to my strengths as a player, because my early instinct was towards solid closed positions, technical play, and endgames, but when I actually played OTB tournaments, I used to play 1.e4 and win games mostly by aggressive tactical play where being much younger than most of my opponents was probably my main advantage.  I used to win a lot of games very quickly on the white side of the open sicilian (despite a total lack of theoretical knowledge), and am really loathe to give that up.  Dry positions probably fit my strengths better, but I find them boring.

I'm facing a dilemma as to what openings I should take up now that I'm coming back to serious play at 35 and intending to take on stronger players who will know their openings well.  The openings I choose now, I hope to still be playing when I'm 50 or 60, so I don't want to choose something super sharp or theoretical that I won't have the energy for as an older player, or would be inviting younger players to out-calculate me.  On the other hand, I'm not too keen to take up boring safe grandad openings.

I guess I'm not asking what openings I should play, or asking for specific lines.  I'm just wondering if anyone else has had to make a similar decision about what openings they want to be playing long term while still trying to improve after the age of 35, and whether old guys can still have success playing open sicilians or if it's time to go back to 1.d4 and start grinding.  At 35, am I young enough to build a sharp 1.e4 repertoire now and go for the grandad openings later, or is it best to start getting experience with them now?  

Also, tell me if my thinking on this is totally wrongheaded, because openings always have left me a bit confused.