2010 RS250 LSD is optional only so check the car specs when you get the reg no or come back here & ask!
2010 RS250 Cup Chassis Pack = LSD as std
2011 RS265 LSD is std
TCE 180 has traction control as std.
TCE 180 is 2010-2011 only it was not sold in 2012.
GT220 does not have LSD at all so probably discount that!
Regarding chipping well the engine design (F4RT) is easily capable of 300-450 BHP! (someone got 500BHP from theirs using an extreme race setup!). Clutch & gearbox though 300BHP is probably close to the limit! I would do the following:
Stage 1 remap to add another 40-50BHP + 60-70NM £400
Exchange the intercooler to a slightly larger model (engine will run cooler last longer!) £600
Put a Hybrid race turbo on it £2K
You can get another 5-7 BHP by just changing the air filter. Turbo BOV are a big no no apparently the turbo will break easily if you do this!
Sports exhaust can add another 10 BHP but cost £500-700!
Do not bother with larger alloys as this means the speedo & fuel consumption reading would be wrong & the ECU is protected from modding!
These few mods would cost you more than the car cost though so make sure you want to keep it for a while!
This green RS I think is a stunning example of what is possible for €30K worth of mods!! Its been sold recently to someone in Belgium the previous French owner spent €10K on the green metallic paint & another €20K on mods like 19" alloys, lowered suspension & several engine mods to give well over 300 BHP!
Bagged Green Renault Megane RS - Accelerations, Sounds, ... - YouTube
For £8K all your going to get is either 2010-11 RS250 or TCE 180. Just settle for that see how you get on with it before thinking about more engine power! They are very quick as standard due to the compact chassis & sub 1400KG kerb weight combined with massive torque! 340-360NM for RS250 & 300-322NM for TCE 180 (renault has a hidden turbo over boost facility as well when you floor it you get a few % more power!).
With regards family members well the RS & TCE180 are 2 + 3. You can easily get 2 adults plus a centre child seat in the back or 3 children up to young teens age (over 6ft is probably too much it would be cramped leg room wise but boot is also surprisingly large for weekly shops school runs etc etc!).
Avoid any which you think might have been used on the track for long as the clutch will most likely be knackered !!! (big money to replace those) look for something which has been mainly normal road mileage.
In france there is a big mod scene but the main website is only in french some great mods done by those owners they really love their Meganes! They get Renault factory support & access as some of the forum members work for Renault! Once you drive one you can understand what makes them great cars (if you choose the right model...most of the diesel range are pretty poor engine wise but the petrol turbo 2.0L range are in another league
). You can spend 2-3 times as much on a german or asian badged equivalent but I seriously doubt you will get 2-3 times road going enjoyment out of them vs a decent Megane
http://www.megane3.fr/