Just my 2 cents;
As someone mentioned, there are a lot of opinions, here is my set up, it works extremely well, remember flyin' is supposed to be fun, I hate to waste time at the field fussing over stuff, flyin time is to precocious!
1. Saito 82 is the way to go, if you don't have the coin for it, save and get it later you'll understand why. I have three, 72 82 and 100, I just purchased a YS 140 Sport for my Funtana 90, so I'll get an opinion on that too! BTW, do the research, you will find that OS 4 strokes are overweigh, over priced and are low Hp. They need to get back in the game. They had a 70 "Ultimate", so many problems the stopped making it. That is a 2" TruTurn Wide Blade Spinner up front with a 14x4W blade.
http://www2.towerhobbies.com/cgi-bin...?&I=LXFBJ5&P=0
http://www2.towerhobbies.com/cgi-bin...?&I=LXGAE5&P=M
2. IF your a Futaba user, S9001 coreless BB servos are great for this plane, $30 @ or 3 for $87. No need for digi's, metal gear, whatever. I just bough some Hitec servos for the F90, yet another pending opinion, but I liked the acc. pack they had vs Futaba's, they give you stickers too!
http://www2.towerhobbies.com/cgi-bin...296&P=ML#mults
3. Great planes fuel valve and "Handy Mounts" - makes fueling easy, sand the firewall and mount with EPOXY, also seal the mount w/ thin ca.
http://www2.towerhobbies.com/cgi-bin...?&I=LXME95&P=7
http://www2.towerhobbies.com/cgi-bin...?&I=LXK135&P=M
4. Remote Glow ignitor - Saitos must have some kind of funny recess in the plug area, I cant seem to remember what I used......ugggg I will let you know.
5. Upgrade the clevises, I think I used Dubro slide locks and "Z" bends at the servos. A nice pair of Z bend pliers is about $12, I have the Hangar 9 brand.
http://www2.towerhobbies.com/cgi-bin...?&I=LXWH33&P=7
6. Hummm..... let me think.
7. Upgrade the tailwheel with the small Sullivan job, $7 or if you use the supplied GP type, run a couple of screws thru the plastic tab in the fuse, remove them and harden w/ CA, put screws back in.
http://www2.towerhobbies.com/cgi-bin...?&I=LXFV46&P=7
8. Custom tail braces - I used the technique and parts list from my Sig Somethin' Extra, see the photos. Here is some of the stuff you will need, looks like a lot but you might have it laying around already, use thin ca for thread lock, it doesn't need to be so tight you pull the surfaces out of wack, just enough so the loads can be transferred during hi G maneuvers to the entire airframe.
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXD838
http://www2.towerhobbies.com/cgi-bin...?&I=LXD996&P=0
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http://www2.towerhobbies.com/cgi-bin...?&I=LXD590&P=0
Here is another option, I always look at it in the LHS, but always end up building my own;
http://www2.towerhobbies.com/cgi-bin...?&I=LXFV30&P=7
See my pics, if you are confused as to the assembly, l could explain it better or just scan in the Sig manual for you, no biggie.
9. Oh yea, I wish I had done this, Seal the gap in the ailerons and elevators w/ clear monokote. Instructions are in the attached Hangar 9 assembly manual from the ultra stick, page 9.
10. Best for last, landing gear upgrade, this is EASY, CHEAP and will AVOID a repair. Use the Dave Brown long reach CA applicators to get thin CA inside where the LG block is, you will NOT be able to see what you are doing, but it's worked for me. Get a lenght of 4-40 rod (smooth), and find a drill bit (I used a tap bit, not sure of the size) and test to find a good fit. Then take the drill bit in a dremel and drill from the inside of the plane, where the front of the wing mounts to the fuse, you will see where GP put some bamboo looking pins in, do it at the same height. DRY fit the rod in and mark correct length, cut 2. Tap the rod in and thin CA from both sides. The goal here is to get the rod near the top of the landing gear plate inside the fuse, where you cant see! You might be able to feel it if you can get your hand in there, or you can look w/ a flashlight from the hole in the firewall and you might kinda see it.