No problem. The i3-6100 gets you to 500. But two cores is going to limit you in the future. It will definitely last longer with the i5 so I'd spend the extra 90.
PCPartPicker part list /
Price breakdown by merchant
CPU: Intel Core i3-6100 3.7GHz Dual-Core Processor (€119.84 @ Mindfactory)
Motherboard: MSI B150I GAMING PRO AC Mini ITX LGA1151 Motherboard (€99.87 @ Amazon Deutschland)
Memory: G.Skill NT Series 8GB (1 x 8GB) DDR4-2133 Memory (€49.43 @ Mindfactory)
Storage: Kingston SSDNow V300 Series 240GB 2.5" Solid State Drive (€77.99 @ Amazon Deutschland)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive (€52.84 @ Mindfactory)
Case: Thermaltake Core V1 Mini ITX Tower Case (€43.89 @ Amazon Deutschland)
Power Supply: EVGA 500W 80+ Bronze Certified ATX Power Supply (€49.70 @ Mindfactory)
Case Fan: Fractal Design FD-FAN-SSR2-80 19.5 CFM 80mm Fan (€6.00 @ Amazon Deutschland)
Case Fan: Fractal Design FD-FAN-SSR2-80 19.5 CFM 80mm Fan (€6.00 @ Amazon Deutschland)
Total: €505.56
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-11-03 16:14 CET+0100
Edit:
Go with the one 8gb stick, then if you need more RAM in the future just drop in another 8gb.
PCPartPicker part list /
Price breakdown by merchant
CPU: Intel Core i5-6500 3.2GHz Quad-Core Processor (€207.81 @ Mindfactory)
Motherboard: MSI B150I GAMING PRO AC Mini ITX LGA1151 Motherboard (€99.87 @ Amazon Deutschland)
Memory: G.Skill NT Series 8GB (1 x 8GB) DDR4-2133 Memory (€49.43 @ Mindfactory)
Storage: Kingston SSDNow V300 Series 240GB 2.5" Solid State Drive (€77.99 @ Amazon Deutschland)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive (€52.84 @ Mindfactory)
Case: Thermaltake Core V1 Mini ITX Tower Case (€43.89 @ Amazon Deutschland)
Power Supply: EVGA 500W 80+ Bronze Certified ATX Power Supply (€49.70 @ Mindfactory)
Case Fan: Fractal Design FD-FAN-SSR2-80 19.5 CFM 80mm Fan (€6.00 @ Amazon Deutschland)
Case Fan: Fractal Design FD-FAN-SSR2-80 19.5 CFM 80mm Fan (€6.00 @ Amazon Deutschland)
Total: €593.53
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-11-03 16:13 CET+0100
Then add a GPU and you have a decent 1080p gaming rig:
PCPartPicker part list /
Price breakdown by merchant
CPU: Intel Core i5-6500 3.2GHz Quad-Core Processor (€207.81 @ Mindfactory)
Motherboard: MSI B150I GAMING PRO AC Mini ITX LGA1151 Motherboard (€99.87 @ Amazon Deutschland)
Memory: G.Skill NT Series 16GB (2 x 8GB) DDR4-2133 Memory (€91.82 @ Mindfactory)
Storage: Kingston SSDNow V300 Series 240GB 2.5" Solid State Drive (€77.99 @ Amazon Deutschland)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive (€52.84 @ Mindfactory)
Video Card: EVGA GeForce GTX 1060 6GB 6GB GAMING Video Card (€267.37 @ Mindfactory)
Case: Thermaltake Core V1 Mini ITX Tower Case (€43.89 @ Amazon Deutschland)
Power Supply: EVGA 500W 80+ Bronze Certified ATX Power Supply (€49.70 @ Mindfactory)
Case Fan: Fractal Design FD-FAN-SSR2-80 19.5 CFM 80mm Fan (€6.00 @ Amazon Deutschland)
Case Fan: Fractal Design FD-FAN-SSR2-80 19.5 CFM 80mm Fan (€6.00 @ Amazon Deutschland)
Total: €903.29
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-11-03 16:17 CET+0100